Batch-execution support in Unity.py

[rtapella]

Likely to require:

• a tag that is used to tag all jobs in a batch (may be user-entered plus some prefix like batch-id-[blah blah blah])
• a way to enter MULTIPLE files as inputs

TBD:

• if you have SETS of files that go together, how do you indicate a list of those
• e.g. file1.jpg + file1.lbl are processed together; how do you indicate this for a folder of files called fileX.jpg and fileX.lbl