Finally solve the bug on Samsung Android 9 and 10 phones that the Dialogs Main & patterns wouldn't be modeless: move the setting of this flag earlier, to the 'onCreateDialog()' function.
Minor.
Lots of bugfixes.
Move to AndroidX, target API level 29.
(Hopefully) make the Dialogs NOT disappear on clicks outside (previously this wasn't working on Android 9).Lower API requirements to 21.
Progress with the 3x3x3 Solver.