Define the Ajax calls behaviors for handling ideas

[abbysmal]

Currently, there is three ajax call implemented:

• reject_idea: Will close the issue, set the rejected label (and wipe all the other labels)
• approve_idea: Will set a ready label (and wipe all the other labels)
• duplicate_idea: Will close the issue, set the duplicate label (and wipe all the other labels)

I guess the first thing wrong here is wiping all previous labels, but it would be nice if we had a clearly defined behavior somewhere, like for example here. :)