Merge pull request #53 from feigner/master

moving pdiff max_attempts assignment before first reference (ResizeWorkflow)
Moves work queue tasks to have canceled and error states; indexes tasks by build, release, run so we can query for their heart-beat status to show to waiting users and find tasks to cancel
Don't retry capture tasks forever if they're getting OS errors.
Adds query to work queue interfaces
Progress on showing most recent heartbeat for run on run page
Trying to make heartbeat statuses work; need cache invalidation signal
Plumbed through evicting cache for run status; still doesn't work client side because we cache too heavily in the browser
Adds canceling the last release attempt's tasks and transitioning its state
Fixing run status pulling info from a dictionary
Simplified pre-fetching of related resources just to be the images of the next run
Remove unused parameter in save admin log