Add support for uploading scrambles

There's now a file chooser for scrambles. It will let you choose 1 or more .zip or .json files that came from TNoodle.

Added a scrambles column to top left chart that lets people choose the scrambles for each round.

Auto "matching" of scrambles to rounds has not been implemented yet. I'm not sure of a good way of doing it. See Scrambles.matchScrambles() for the right place to implement this.

Unfortunately, I added no tests =(.

Note that this code will *not* work with files generated by the current version of TNoodle. That's because I changed the poorly named "scrambles" attribute to "sheets" (see https://github.com/jfly/wca-workbook-assistant/blob/master/src/main/java/org/worldcubeassociation/workbook/scrambles/TNoodleScramblesJson.java#L6).