server.py: Properly check if the user is one of the reviewers
Only consider the statuses created by Homu
Properly process queue when merge conflicts happen

If start_build() returns False, which means that the build could not be
started, proceed to the next item instead of breaking the loop.
Use Jinja2 to render HTML
Comment on the pull request whose status is changed
Insert pull request number instead of head SHA into merge commit message
Display mergeability in the queue
Add the assignee field to the queue table
Create rollup pull requests using OAuth
Merge remote-tracking branch 'bar/master'