Refactor invite

[yeukhon]

Finally got a few hours tonight to finish this! Refactoring went pretty smoothly. Manual testing is time consuming.

• refactored the invites/control into resend, decline and accept apis
• refactored common code into load_user_and_invite and invite_has_expird
• extend invite lifetime when resend instead of issuing a new id

This requires mozilla/minion-frontend#140 to be pulled in.

[st3fan]

I don't think this is an appropriate solution. First of all, the error reporting does not work. You call jsonify to create an error rrsponse but it is never returned. If you have to return it then the contextmanager would have to return a tuple with (error, invitation, user) which does not seem to be the right thing. Context managers were not really intended for this kind of code.

I would prefer to simply see load_invite and validate_invite functions that return an error if the invite is bad.

[yeukhon]

Hmmm the nice thing about this contextmanager "hack" is it allows us to do enter and exit. I probably could do decorator @ but i have to re-read both documents which is resource wasteful. I do this initially because I kinda want to move away from the C-like style where we do

user, invitation = func(...)

I think we can do that. I was hoping to find a api-level enter, exit scope. Maybe thats what class api is for :)

Let;s remove context manager then.