Add basic redirects app and admin panel.

This only supports basic prefix-level redirects for now.
We will work on a more flushed out grammar for this soon. 

Refs #812
Only support a subset of redirects for now.

We’ll add the Advanced/grammar part later.
remove SERVE_MEDIA concept.
Missed utils in the previous commit.
Need to define it before we check for it :)
Spruce up the admin page.
Remove pdb and fix non-existent variable.
Add tests to redirect app
Fix project_slug not existing.
Fixes from Anthony's review
Fix re-defined to variable
Remove redirects test for now.
Always have project exist too.
Allow passing of variable to run tests
Merge pull request #870 from rtfd/redirects-app

Add basic redirects app and admin panel.