Progress on New Save Format

Integrated the base code for our new save format. It still needs more
work but at least some substance is there. Ignore the file not found
messages that come up when trying to save the world's data - since we're
not actually writing files, an exception occurs when we some later code
tries to move non-existent save files.

Also moved the FileFilter functionality out of DungeonHelper and into
its own class, FileFilters, since it's finally needed more broadly.