More pythonesque check for there being no flash messages.
Refactor the compilation of less files.

This achieves a few goals:

1. You can now have multiple less files, matching the glob 'app*.less'. The
   less watcher and the compile_static command will watch/compile them all.

   This means you can break your rules up into multiple less files - useful if
   perhaps you only want to load some rules (e.g. admin rules) on certain
   blueprints.

2. You can also have less files that don't match the glob above. These are
   assumed to be imports that are imported by one of the files matching the glob.
   If the less watcher spots them changing, it recompiles all the files matching
   the glob.

3. Gave the less compiling stuff its own logger. Also, we now log each file
   that is being compiled.

4. Tighten up the event listening criteria in the less watcher, so that saving
   a file in vim doesn't trigger a triple-compile.
Add an 'anonymous activity timeout' to identity sessions.

This allows sessions that aren't for logged in people to be a different length
than those that are for logged in people.

The aim is to keep the number of identity sessions from growing too much if a
site has a lot of anonymous usage, but also a high activity timeout.

You probably want to set this to as long as might be necessary for any use of
the identity session that an anonymous user could plausably want. This could
potentially be nothing, in which case the default of 15 minutes should be fine.