Add timestamps to output folders.

[senderle]

Rather than overwriting output, save to files and folders with timestamps.

[senderle]

Elaborating on this: let's have the output have this structure:

[user-selected folder]
    tmt-output-[YYYYMMDD-formatted-timestamp]
        csv
            blah.csv etc...
        html
            blah.html etc...

[senderle]

I think I delayed merging this to master because I was concerned it would be a "breaking" change, and wanted to delay it to a later major version. Now I'm not sure what its status is; it may be in master but commented out, or it may need to be merged. I'll add notes here if I get a chance to investigate. If people want this feature I'll move it up in the queue; but otherwise it's a lower priority now.