Add support for cancelling selected steps in a running study

[jsemler]

Expand Maestro to support cancelling selected steps in a running study.

Example API:

$ maestro cancel <path/to/study> --steps <step-name>

$ maestro cancel <path/to/study> --steps <step-name1> <step-name2>

[crkrenn]

A closely related request would be to include job ids in "maestro status"

[jwhite242]

+1 for jobids in the status, even if optional

For cancelling, is cancelling a step name intended to be al paremeters of a step, or individual parameter combos?

[FrankD412]

I can definitely get behind a job identifier column in the status table. The StudyRecord already has that information. The only limit is that if a job has a restart, then it will only display the last assigned job identifier.