Adds "Topic editing only" along with the tooltip explanation to lower right
of message editing box when it's past the message content editing deadline.
This is controlled through the admin tab and a new field in the Realms table.
Notes:
* The admin tab setting takes a value in minutes, whereas the backend stores it
in seconds.
* This setting is unused when allow_message_editing is false.
* There is some generosity in how the limit is enforced. For instance, if the
user sees the hovering edit button, we ensure they have at least 5 seconds to
click it, and if the user gets to the message edit form, we ensure they have
at least 10 seconds to make the edit, by relaxing the limit.
* This commit also includes a countdown timer in the message edit form.
Resolves#903.
This change would allow anyone in the realm to set a topic for a "no topic"
message. As soon as the message topic is set, only the sender can change it again.
(imported from commit 0a91a93b8fd14549965cedc79f45ffd869d82307)
Rishi Gupta
Brock Whittaker
Umair Khan
Waseem Daher
Steve Howell
Leo Franchi
Kevin Mehall
acrefoot
Tim Abbott