Add journalist topics

Users can select topics when creating a journalist.

NOTE: Creating new topics will be covered in separate commit. This feature is currently using pre-defined topics.

Trello: https://trello.com/c/OdlUwErr/47-add-topics
I just re-loaded my repositories on https://houndci.com/ and re-selected this one. I'll try pushing again with a white-space to test.