Cleanup: removed dead code
Added 'announcement' page type

This is a hackish way to create a special regular page, and most of its
singularities are specified in view code. Announcements are not an entity
of their own and they are represented as static pages in the model and
database level. Not the cleanest and fanciest way of doing this, but since
these special pages are a temporal workaround, it's a trade-off we can
make.

Part of #59.
Display announcements in a sidebar

Part of #59.
Remember sidebar's expanded/collapsed state

Part of #59.
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 #59.
Cleanup: removed dead code
Docs: added page about supported browsers
Docs: document latest changes to refresh_stats command
Docs: document the newly-added test_checks command
Cleanup: coding style fixes
Provide a more self-explanatory description
Rather use `get_profile()` on the `User` object
Use iterators to avoid filling the built-in queryset cache
Rewrite links according to the current context's language

Part of #59.
Implemented project notifications using static pages

Fixes #59.