Some languages such as Japanese use different word order with
English. If the stream name must be the last word, translating to these
languages is difficult.
Following strings are marked translatable:
- All strings which are passed to `button.text` or which affect the
text of buttons.
- All strings passed to `placeholder`.
- All strings passed to `compose_error`.
Fixes#969
Add javascript to handle the button clicks and update the status based
on the subscribe and unsubscribe events from the server.
(imported from commit 6b9c0b40d9084e3d8b64bed701ebc786bef6d432)