emails: Set alt attribute to empty for leading images.

The alt text of the leading images were displayed as preview
content in inbox by email clients like gmail. Since the leading
images were used mostly for decoration this made the preview
content gibberish. It's fine to set the alt attributes to empty
from accessibility point of view since the old alt attributes
did't added any meaningful information.

templates/zerver/emails/confirm_new_email.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/email_logo.png" alt="{{ _('Zulip logo') }}"/>
+<img src="{{ email_images_base_uri }}/email_logo.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/confirm_registration.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/registration_confirmation.png" alt="{{ _('Turtle with envelope') }}"/>
+<img src="{{ email_images_base_uri }}/registration_confirmation.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/custom_email_base.pre.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/email_logo.png" alt="{{ _('Zulip logo') }}"/>
+<img src="{{ email_images_base_uri }}/email_logo.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/find_team.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/email_logo.png" alt="{{ _('Zulip logo') }}"/>
+<img src="{{ email_images_base_uri }}/email_logo.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/followup_day1.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/email_logo.png" alt="{{ _('Zulip logo') }}"/>
+<img src="{{ email_images_base_uri }}/email_logo.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/followup_day2.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/day2_1.png" alt="{{ _('Octopus box with heart') }}"/>
+<img src="{{ email_images_base_uri }}/day2_1.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/invitation.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/registration_confirmation.png" alt="{{ _('Turtle with envelope') }}"/>
+<img src="{{ email_images_base_uri }}/registration_confirmation.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/invitation_reminder.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/invitation_reminder.png" alt="{{ _('Mailbox with envelope') }}"/>
+<img src="{{ email_images_base_uri }}/invitation_reminder.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/notify_change_in_email.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/email_logo.png" alt="{{ _('Zulip logo') }}"/>
+<img src="{{ email_images_base_uri }}/email_logo.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/notify_new_login.source.html

@@ -5,7 +5,7 @@
 {% endblock %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/email_logo.png" alt="{{ _('Zulip logo') }}"/>
+<img src="{{ email_images_base_uri }}/email_logo.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/password_reset.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/email_logo.png" alt="{{ _('Zulip logo') }}"/>
+<img src="{{ email_images_base_uri }}/email_logo.png" alt=""/>
 {% endblock %}
 
 {% block content %}

templates/zerver/emails/realm_reactivation.source.html

@@ -1,7 +1,7 @@
 {% extends "zerver/emails/compiled/email_base_default.html" %}
 
 {% block illustration %}
-<img src="{{ email_images_base_uri }}/registration_confirmation.png" alt="{{ _('Turtle with envelope') }}"/>
+<img src="{{ email_images_base_uri }}/registration_confirmation.png" alt=""/>
 {% endblock %}
 
 {% block content %}

version.py

@@ -26,4 +26,4 @@ LATEST_RELEASE_ANNOUNCEMENT = "https://blog.zulip.org/2019/12/13/zulip-2-1-relea
 #   historical commits sharing the same major version, in which case a
 #   minor version bump suffices.
 
-PROVISION_VERSION = '67.1'
+PROVISION_VERSION = '67.2'