Add status enum to `Competition`

Different actions are possible at different stages of the competition.
Add `formatastic_bootstrap` gem

Includes the formtastic gem and configures its output to be compatible
with Bootstrap
Re-add competition scaffolding

Comes with a basic competition creation form.
Permit `Competition` parameters in controller

This allows competitions to be created and updated successfully.
Use a primary button in the Competition form

It looks a bit nicer.