Minor changes to scrumbugz to get it to work with bugzilla 4.5.x, additional settings, work towards http only bugzilla integration

Currently, there are a few minor issues w/ scrumbugz and bugzilla 4.5.x

1. Bug.get proves an 'update_token' on retrieving a bug while logged in. Ignore this for now

2. Bugs with an unspecified priority return '---' which exceeds the limit varchar(2) for Bug.priority in Bug model. Increase the length of varchar to 3

3. Additional settings in settings/base to configure bugzilla urls/auth

4. Work towards http only support for bugzilla in scrumbugs. Currently, scrumbugs uses SessionTransport(xmlrpclib.SafeTransport) which is https only. Changing it to xmlrpclib.Transport causes bugzilla to throw errors about requiring login for various xmlrpc methods.