Not all preference changes need to trigger a shuffle

[fcarsten]

Currently any changes in the Preferences screen triggers a re-shuffle. This is not strictly necessary for all the changes and some could continue with the current board.

[fcarsten]

Now only change of dictionary and whether 3 letter words are allowed requires a game restart.
Not requiring restart after changing whether 3 letter words are allowed would be possible, but a bit more work, Probably cleanest solution would be to keep separate list for all words which were entered/computed and which words are displayed.