Draft: (3) Create internships

Depends on !583 (merged) and !584 (closed)

Adds internships support (work done by @ywang46 )

TODO:

• Remove duplication by actually reusing modals and controllers from project (refactor away the @project references / set @project in the internships controller)
• Add way to get correct route for project type (internships go to different controller, reuse logic?)
• Fix problems