checker: use elif to save on config['scm'] checks

viewer: remove special case for cleanup task collapser Now that final "job finished" metadata line is not in any task, cleanup is empty and won't get the collapser naturally.

adapters: add GithubAdapter

checker: support git

checker: raise the exception after bad_exit()

checker: move hg calls to separate functions, check config['scm']

models: revs are not unique, can be nulls Revision numbers can change depending on --branch or --rev for hg clone.

incoming: job started/finished metadata lines are not in any task

models: manual_upsert() to create new instances or update existing

models: use a simple heuristic to pick HgwebAdapter