Luigi task list status view with dependency graph
Changes to graph API for use in new visualiser
Tasks grouped by type, tabs for graph display
start on task_list
Task list API call, test for dependency graph API call
New tab-based interface with #-urls. Talks to Luigi properly
Add upstream_failure field in task retrieval API.
Reseting server to fix tearDown issues. Also changing remaining
DummyTasks to use task_id instead of id to fix failures.

Change-Id: I10b19aabafe069d6c1f699ecf1c06afaf918f97c
Filter on upstream_status.
Adapted front end to work with API
Ignoring task ids that we don't have in _tasks

Change-Id: Iad57bd94fecaa9a47074015aff12d2649cbc98c9
Improve API testing
Visual tweaks
Adding memoization to the upstream status checker

Change-Id: I0d2a69fff0eb047e4a9fd60b96c4b3f6f776d7b8
New hand-written layout engine more suited to directed acyclic graphs (like dependency graphs)
Removed dependency on D3 and brought library dependencies in-repo