Added screens.
Merge branch 'develop'
Readme.md: added screenshots.
tracbuildbot/admin: added "https" support for "buildbot server" field.
tracbuildbot/buildbot_api.py: added support buildbot url with sub_path (like http://my_server/buildbot).
tracbuildbot/buildbot_api.py: BuildbotConnection.reconnect() - added missing slash in pre_path.
tracbuildbot/timeline.py: BuildbotTimeline.get_timeline_events() - self.cache.tmp_path not useful, removed.
tracbuildbot/buildbot_api.py: BuildbotConnection._request() added httplib.HTTPException catching.
tracbuildbot/timeline.py: fixed build url.
tracbuildbot/buildbot_cache.py: fixed additional caching if last_cached_num is 0.
tracbuildbot/admin.py: fixed builder url.
tracbuildbot/buildbot_cache.py: fixed last_cached_num initialization.
tracbuildbot/buildbot_cache.py: async_buildbot_cache_worker() - fix - when error of caching of one builder interrupts whole caching.
screens/admin.png: updated.
tracbuildbot/buildbot_api.py: improved request performing.
tracbuildbot/web_ui.py: added BuildbotJsonApiHandler to load info for buildbot_page instead of direct way.