Data & GUI Cleanup

This update includes:

- Many bugs fixes, including fixes for audio looping and dark mode forms.

- Data has been moved from ProgramData to a split between Program Files (where Campaign Manager now installs its data files) and the user's AppData folder (where the user can extend the data).

- The library of textures for the map creator can now be selected as a map background (without first creating a map from them).

A promotional video has also been created demonstrating some of the features of the software!