Adds auto-imports to shell_plus.

This uses django-extensions's SHELL_PLUS_POST_IMPORTS.  It also bumps
the django-extensions version to 1.2.5, since SHELL_PLUS_POST_IMPORTS
only does anything in >=1.2.3.  The only known backwards-incompatibility
is to UUIDField, which we do not use, so this should be safe.
Adds some more imports, and fixes esp.program.modules.models import.
Add UserBitImplication import which was failing
Merge pull request #885 from learning-unlimited/shell-plus-imports

Adds auto-imports to shell_plus.