Cancel Tasks capability

[Viqsi]

From Veronica's todo document:

• Add way to cancel a submitted job/query

There's an attempt at allowance for this in API calls in diverweb, but otherwise the UX doesn't exist at all and there's no way to do this with the API. Indeed, I'm not entirely sure how we would do that, since API calls are supposed to be independent of another. Would require significant research.

[WValenti]

The ONLY think I can think of is something that very clearly contacts one of us with details on the "runaway" process so we can use KILL on it after we confirm with SHOW PROCESSLIST.