Small Character Improvements

This PR removes the character's show page #109, and with it the ability for users to delete their main. Previously there was a bunch of gross logic attempting to handle it. Now instead users simply cannot delete their mains. Also users cannot switch mains anymore. This is something I decided would be smart because it prevents users from randomly starting to show up as anything person on the site. If someone wants to change their main, now they must talk to someone (me) and get it fixed.

Also I made a `has_one` relationship for the `main`. This should allow for faster calls for the users main attributes in collections by using `includes(:main)` instead of `includes(:characters)`.