cache gitolite info, refresh in background process

Calling "ssh git@GITOLITE_SERVER info" on slow connections can
cause timeouts.  Gitolite's response is now cached for longer
time and refreshed by a background process.
- New module: webui.gitolite.
- Moved webui.get_repos_orgs() to webui.gitolite.
- New task: gitolite_info_refresh.
- Now assumes that DDR.gitolite_info returns raw Gitolite output.
Merge branch 'cache-gitolite-info' into develop