Split settings and moved SECRET_KEY to env.

Having SECRET_KEY and other parameters in an environment value is safer
and more fliexible. I'm trying to follow the principles of the 12-factor
app.
Fixed path mess that came from putting settings in a package
Remove unnecessary requirement.
Merge remote-tracking branch 'upstream/master'
Run tests in in-memory sqlite3, it's much faster.

We should still run them on Postgres from time to time to track DB-level
bugs, especially in transactions and relational integrity.
Added better error messages for templates. (I don't think this actually does anything, because we're using jinja.)
Fixed a settings manipulation that was breaking other tests.

The manipulation of ASKBOT_EXTRA_SKINS was breaking widget_tests and
post_model_tests when running the full askbot test suite.