Project bot (Fix #332)

The intention here is to
* Create an "edit bot" account for every project that has at least "push rights" to the given project to perform specific action on the behalf of an otherwise non authenticated user.

I *think* it requires an account with "admin" permissions to get a list of authenticated users for a given project, so I decided to take a more "hackier" approach:

1. Try to perform the action on behalf of the current logged in user and if this "fails"<br />
1a. Try to perform the action on behalf of a configured "edit bot"

When the status changes (`open` <=> `closed`) a comment will be generated that includes the username of the user that performed the action.

This should be carefully reviewed and tested (how?) before merging into master. :wink: