add notification on job finished

[erwindon]

Is your feature request related to a problem? Please describe.
currently, the SaltGUI screen is mostly static. it typically refreshes only on request.

Describe the solution you'd like
Jobs that just finished should leave a notification on the screen.

• add to top of Jobs side-panel
• add to top of Jobs page

Additional context
showing just a few latest jobs prevents that screen must be refreshed.
e.g when:

• a background job was started and the command-box already closed
• someone else runs an interesting command.

implement by catching events

TODO
there is no "end-job" event, only an "end-job-on-minion"
this makes it hard to detect the end of a job
alternative:

• collect JIDs from "end-job-on-minion" events
• wait 3 seconds after the last update from a given JID
• request the job status
• when job is finished, report it
• otherwise just wait longer