Provide API for inspecting the backend data

[robacarp]

Currently inspecting the backend data requires querying the backend directly. It would be nice to be able to ask mosquito's backend for data about:

• [x] The current list of queues (#153)
• [x] The current list of job runs (#153)
• [x] A list of active runners overseers (#150)
• [ ] Statistics about a runner
  • [ ] How many tasks have been finished in the last hour,minute,second (#156)
  • [ ] How many tasks have succeed or failed in the last (#156)
• [ ] How many tasks have been enqueued in the last hour/minute/second (#155)
• [x] What a runner is currently doing (#147)
• [ ] JobRuns that have recently failed or succeeded
  • [x] The parameters given to a job run (#148)
  • [ ] when it was started (#157)
  • [ ] how long it took to run (#157)

Prototyping for these features is being monkeypatched in the TUI Visualizer project.

[robacarp]

Closing in favor of milestone