Much kinder Crop Plan Manager dialog and behavior
Handle NumberFormatExceptions in cropDB; 'merge' dialog changes from google-cal branch

* also first try at centering dialogs
Keep all dialogs w/i the program window.

* fix filter dialog display issue
more dialogs and error handling

* catch NumberFormatEx in CropPlan
* refactor ErrorDialog
* convert some silent error to error dialogs to clue in the user