Fix typo

Thanks to oneuser_
Move to django 1.7 with built-in db migrations

This moves clears the old south migrations and replaces them with (one) intial
django migration.

Fixes #99
Cleanup global settings file

This better groups different settings together and as a nice side effect,
makes the 1_6.W001 warning go away.
Explicitly set 'exclude' for ModelForms

In django 1.7 creating ModelForms without either a 'fields' or 'exclude'
raises a deprecation warning.
Colour code the workout calendar

If a log has an impression, the day is coloured accordingly (greed for
good, etc.). Additionally, with this change the calendar uses more bootstrap
classes.

Fixes #98
Improvements to calendar view