Do cool stuff with `team <-> project`

[emcoding]

Blocked by ~#816~ #892
Once the production db is updated with the team.project_id, we can use the team <-> project association for things like:

• [x] 1 Orga Team edit page: assign project with dropdown select
• [x] 2 Use the association in the query Projects#index
• [ ] 3 Turn the project_name in team#display_name into a link to the project show view.
• [x] 4 Change relevant references to the team.project_name into team.project.name
  ... ? << Add your Wishlist here

Maybe split it up in separate PR's.

[mkalininait]

In addition to 1: I think we should remove the project_name from the non-orga team edit page.

And this comment, too: https://github.com/rails-girls-summer-of-code/rgsoc-teams/issues/19#issuecomment-322031515