Team doesn't show in team switch form when full

[jessie-jin]

Fixes #27

Checks if the number of dancers on the team is greater than the maximum size every time a dancer is added or dropped. If it is greater, then that team won't show up on the team switch form. Once the number of dancers on a team becomes less than the maximum size, the team appears back on the form.

[yu-alan14]

There are a few bugs with this branch.

1. If a database is initialized with dancers, and there are more dancers on a team than the max size,the team will still display on the team switch form.

2. This one has a higher priority: when using the team switch form tab to switch dancers onto a team, by approving a team switch request, the display fields will not update.

Reproduce the bug:

• have 2 teams with max team size 2 and 3 dancers
• put 2 dancers onto team 1 (at localhost:3000/admin/dancers)
• put 1 dancer onto team 2 (at localhost:3000/admin/dancers)
• visit localhost:3000/admin/teams and see that one team has display = yes, while the other does not
• create a team switch request at localhost:3000/teamswitch for one of the dancers on team 1 onto team 2
• approve the team switch request at localhost:3000/admin/team_switch_request
• visit localhost:3000/admin/teams and see that both teams are now locked