Implement clue list positioning suggestions from issue #101

[swerthei]

Implements items from issue #101.

• When the clue list is first entered, position the list to the entry that was current on the play board.
• When moving to a different clue in the clue list, position the highlight to the first non-blank letter in the word. If none, then position to the first letter.
• Add menu bar items on the clue list to scroll to the next or previous unsolved clue in the list.
• Make left/right arrow movement in the clue list not be dependent on the current movement strategy set in the play board.

This is my first contribution so please give feedback on style or anything else.

Thanks