We don't need no button for copying. (clicking the URL is enough.)

At least imo; discuss & revert if you disagree.
Got rid of easily confused characters in game ID: 1, I, l and O.
Super-slight DRY cleanup.
Better error reporting of invalid flags.
Added a chaotic card layout option.

Is golang's rand.Intn not uniformly distributed, does my use of it
trash the uniformness, or did I just have a bunch of "bad luck" runs?
Make the card rotation option work.

Refactored a bit of the syncing buttons with inputs code on my way.