fix numerous bugs re: grid size, cell positions, overlaying in bg.BG()
DVD.get_matching_file(): update search logic for better results, esp with multiple vids per directory
add default values to the help text of some options that were missing default info
change output paths (move some items to tmp_dir)
BG(): default to no_prompt
BG(): apply borders to button imgs before creating labels (allows slightly wider label size)
BG(): check for existence of menu labels before getting grid size
BG(): fix several parts of button resizing logic