Web view revamp

[agis]

Backend

• investigate if we can determine when job has started without looking at the path's mod time. Maybe through build_result.json.
• properly display docker build logs (Parse logs from docker build #37)
• properly format "started at" in job/show
• view: dynamically iterate on build result and print it
• make broker package SSE-specific (maybe this is just a rename), also try to make it simpler
• introduce package webtailer (provides the HTTP handlers and uses package tailer & broker)
• extract presentation logic to a separate struct, if necessary
• make job show handler return a consistent JSON (ie. JobInfo type)
• show all job fields when marshalling to JSON
• check for current jobs (job index) in a goroutine, once for all clients