Got a good start on integrating greta

Created a couple of classes to abstract the repo creation process,
created a view that allows users to create a repository, added some
buttons to the competition siebar, and made some updates to the admin
interface.
Repository permissions are set up, as well as repo permalinks
Created a template tag to prettify repo names
Added logging and catch some DNE errors
Can't create a repo if you already have one
Only show sidebar buttons when it makes sense
Clean up repository name in tree breadcrumb
Gray out competition navbar button when viewing repos
Merge branch 'feature/greta-integration' into develop