Implement missing pieces for cancel build

We allow to cancel only created builds at this point.
Allow to cancel jobs after they're started
Properly handle job:canceled event
When observing all builds don't request them

We use `allBuilds` to observe new incoming builds, so we can put new
builds into the lists (for example when build is started). We use it for
observing purposes only, so we actually don't need to get builds from
the server, we can just register record array and use it later on.
Don't require sidebar controller