Comment 0 for bug 4976

When someone tries to join a team, he/she should be able to type in a comment, like _why_ he/she should be member of that team. I'm administrator for the Dutch translators (ubuntu-l10n-nl) and it'd be really neat if - when a user tries to join a team - he or she gets a question (defined by the administrators of the team if they enable this feature) and can comment on it. For the Dutch translators, we'd ask if they have previous experiences, and where. The user can then answer this question, and when the administrators review member's approval, they see this, and use this to judge.

What needs to be changed:

* Joining a team - now with a text from the administrators, and a comment box
* Extra option for team administrators: enable/disable jointeam-comment and have a text for it
* Approving members - now with the comments from $user

Why this is great

It's easier for me, and stops people who are new to translating to (try to) join in the first place.