Docs: added page about supported browsers
Followup: Record in release notes that we only support latest browsers
Display announcements in a sidebar

Part of evernote/pootle#59.

Pick notes: Minor adjustments in translationproject views.

Conflicts:
	pootle/apps/pootle_translationproject/views.py
Remember sidebar's expanded/collapsed state

Part of evernote/pootle#59.

Conflicts:
	pootle/apps/pootle_translationproject/views.py
Force expand the sidebar when announcements change

This is controlled on a per-project basis and overrides the user's choice
of keeping the sidebar collapsed or expanded.

Part of evernote/pootle#59.

Conflicts:
	pootle/apps/pootle_translationproject/views.py
Partial pick: Cleanup: coding style fixes

Pick notes: Part of the changes were already done, and the changes in the
    management commands don't apply because we either changed most of its
    code or we still didn't add the command (test_checks).

Conflicts:
	pootle/apps/pootle_app/management/commands/refresh_stats.py
	pootle/apps/pootle_app/management/commands/test_checks.py
	pootle/apps/pootle_store/models.py
	pootle/apps/pootle_store/views.py
	pootle/apps/pootle_translationproject/models.py
Rather use `get_profile()` on the `User` object
Rewrite links according to the current context's language

Part of evernote/pootle#59.
Partial pick: Fix bux introduced in [62eabe8], add invalidating cache for last_updated flag

Pick notes: The change in TreeItem was already picked. The change in
    flag_for_deletion doesn't apply since we removed that code. The
    remaining change was picked, but with some minor changes.

Conflicts:
	pootle/apps/pootle_store/models.py