Weblab: fix Start Over and add version history test

[cpirich]

• When selecting "Start Over" from the Version History dialog, Weblab would proceed to delete all files, but using the current project version, meaning that it would overwrite any changes made during that browser session with the empty project. Non-files-API code avoids this by forcing a new version when resetting the project. We now do the same for Files API projects by ensuring that the call to FilesApi.deleteAll() always generates a new version (using basePath() for the URL instead of basePathWithFilesVersion())
• Added a weblab version history UI test. Unfortunately, it can't peek inside of the bramble IFRAME due to cross-domain restrictions, but we can at least verify that the proper number of unique versions are being created after we: (1) add a file, (2) save, (3) reset the project, (4) choose to restore the version after we first saved with the new file.

[islemaster]

We usually try to avoid arbitrary wait times in UI tests because they're more brittle than waiting for a particular element to appear. I understand that might not be possible in this test due to the cross-origin issues - is there anything we can watch for at this step and the one below?

[cpirich]

Yes, it is definitely tough to wait on something that we can't see. If we figure out cross-domain access, it will help UI tests for weblab for sure!

[islemaster]

I've never seen the general sibling combinator selector before. TIL.

[islemaster]

Awesome, thanks for adding a UI test covering this behavior. I wonder if there's any way around the iframe stuff - you'd think the selenium driver, since it simulates user interactions, could reach anything loaded on the page (though it makes sense that our javascript-dependent steps wouldn't work).