Update job status while running

[svengato]

[svengato]

Solved locally by wrapping the job in a promises::future_promise() (from promises 1.2.0). However, on dev-legfedorg (running R 3.5.2 and earlier packages like promises 1.0.1) this does not exist. Using future::future() instead seems to work, though this is described as "leaky".

[svengato]

Suggestion: add a Cancel Annotation button (while the job is running), as in the Drupal version.

[svengato]

First cut at implementation - commit 5bb6372. Keeping open in case any problems come up.

[svengato]

Cleaned up in commit 64ddb53.