fixes bug 962264 - Switch to native bugzilla API instead of BzAPI Proxy

This was almost embarrassingly simple once I realized how little needs to change. However, it took me some time to get it tested and it took some time to realize that the bugzilla cron app can't use the new REST API because of it taking some 15-20 times longer due to [1035804](https://bugzilla.mozilla.org/show_bug.cgi?id=1035804).

@rhelmer r?