Magic Cube

Very important bugfix for an issue which probably has been the reason for many mysterious behaviours in the past: the JsonReader class cannot be a singleton! Convert it into a normal 'instanced' class.
With it being a singleton there's a major issue: when we create a new TwistyObject from a JSON file (by, for example, going to PurchaseActivity) and then we come back to the old object (by, for example, going back to the main RubikActivity) - then the JsonReader inside the old object has read the new JSON file and thus many of the 'abstract' methods in the old TwistyObject (for example getShortName()) all of the sudden start returning new values!

IAP: finish the 'Purschase' activity.

IAP part 5: new 'Purchase' activity (cont'd)

IAP part 5: new 'Purchase' activity.

IAP part 4: further progress with locks in the object popup screen.

IAP, part 3: non-free objects appear in the popup with a lock icon: make the lock icon's size resolution-independent

IAP, part 2: unify the way we create object popups in ScreenPlay and ConfigActivity.

difficulty icons.

config: license.

Do not crash when something's wrong with the JSON file - handle this gracefully, do not change the object then, and report this to Firebase.