Login templates

Basic blocks, specifically fully working login, registration, image, and content blocks. Specified blocks are working except for:
- I think the CSS needs moved. 
- Default fixtures.
- Tests.
- Easy to use admin.

Please review.

**Important Note**: All html is assume safe. This is probably not non-very-very-trusted user friendly.
After talking with Jason, it seems like returning None is probably the best. Returning None is just a signal that even though a block can handle post data, it wasn't able to do anything with the post or doesn't need to do anything special with the response. 

Returning a fake/empty response won't get us much, other than making the return value more consistent. In the case that it's being used right now there's not much to gain from a consistent return value.