Added Zinnia blog

Lots of copied template files added. Homepage has new blog slider - but
needs revamping probably as well.
Updated Heroku-related requirements
Improved ordering of committee positions
Added Long Road pictures
Started a Staging release fabric task

Not tested/complete
Fixed an import-ordering bug

Had to move Zinnia forms out of the core.forms module
Merge branch 'blog'
Improved blog category admin interface