Major fix to mobile touch screen interaction where touching wouldn't properly line up with the elements on screen. The short version is that Godot's ability to detect "Button is at x position" is horrible the instant the phone isn't the perfect size for the application. All positional references have been gently eradicated from the code and replaced with more foolproof Godot input logic checks.

Also, increased the experience required to master a word, slightly decreased the amount required to add new words, and slightly increased the exp penalty for wrong answers. While playing my own game, I realized I was mastering words just a bit too fast, before I felt I really mastered them, which was also causing the pool of words to stay small enough that process-of-elimination was too reliable. This should make mastery feel more earned. 

Fortunately I was wise enough to anticipate that I might tune the exp values, and so old save files can safely interact with the change. However, previously-mastered words will be put back into the word pool and need a bit more experience to become re-mastered. It's probably good review in any case.