Recurrence

This MR includes the changes from !794 (closed), !793 (closed), and !796 (closed)

Recurrent proposal navigation

This is shown on the project show and edit pages as well as the admin panel.

Making a proposal

Editing

Deletion

When a project cannot be deleted:

Closes #453 (closed)

Closes #454 (closed)

Closes #449 (closed)