This refactors and fixes unicode issues where entities don't display
properly due to being a special character that seems to be rendered
incorrectly in a non-deterministic way every time.
This either removes aria-hidden=true assignments from buttons with
text, or adds a span to only hide the 'x' symbol rather than the
button for closing buttons.
This removes the old base button style which was a blue button and
kills the unnecessary .white class which was essentially just acting as
the new button base.
This then removes all references throughout the settings/subscriptions
pages to those button styles.
This also fixes the strange button styles that changed the :hover and
:active opacity to 0.05 which led to unpredictable results on various
backgrounds.
This makes it possible for Zulip administrators to delete messages.
This is primarily intended for use in deleting early test messages,
but it can solve other problems as well.
Later we'll want to play with the permissions model for this, but for
now, the goal is just to integrate the feature.
Note that it saves the deleted messages for some time using the same
approach as Zulip's message retention policy feature.
Fixes#135.
Brock Whittaker
Vaida Plankyte
K.Kanakhin