super restyle the competitions show page

after adding the teams to it the page felt very underwhelming.
update the competition forms

some of the updates I made when styling the competition show page
affected the layout of the whole site, so the competition form pages
needed to be updated. I also made the submit buttons looks more
consistent with the rest of the site.
add a callback to close connections to the db

apparently Sinatra doesn't handle this automatically, at least for
Postgres. I'm not 100% sure this is a good solution but I'll keep it if
it works.
ensure that Team members are unique

this will be a pain moving forwards to test future features, but it's
silly to have someone sign up multiple times for the same team.
eventually I'll put something in place to ensure team leaders can
control signups for their team.