Bug fixes

This was another "lots of bug fixes under the hood" release.

- When you try to Load or Continue, several bugs would crop up if you canceled the file dialog. Sometimes your game would load an empty file and crash. Sometimes your browser would keep opening the dialog. Even if it did cancel cleanly, canceling a second time would definitely crash. This is real reason I'm pushing this out now.

- I've started expanding the engine to handle multiple campaigns. It's nowhere ready for that yet, but the first thing is to allow different movement and attack icons.