This commit adds a "Followed topics" row to the 'Notification Triggers'
table in the 'Personal settings > Notifications' panel and the
'Organization settings > Default user settings' panel.
This adds support to control email, push, wildcard mention,
visual desktop, and audible desktop notifications for messages
sent to followed topics by toggling corresponding global
notification settings.
The "Followed topics" row is available in the development
environment only.
Updates frontend user-facing strings with "private message" or "PM" to
use "direct message" or "DM" respectively instead.
Note that this updates translated strings as well as a few that
are not translated like search suggestions.
Updates `tools/lib/capitalization.py` for some specific strings
that are impacted by these changes, and removes "PM" and "PMs"
from checked strings.
This lets us simplify the long-ish ‘../../static/js’ paths, and will
remove the need for the ‘zrequire’ wrapper.
Signed-off-by: Anders Kaseorg <anders@zulip.com>