Borders

10 border images.
Rewritten item support so item rules can be shown and disabled.
Display the internal "key" of unknown spell/item.
Display the source of item rules.
Added font options in a theme panel.

Also moved the color options in this new panel.
Fixes GH-50.
Removed dead code.
Moved more functions into Utils.lua.
Moved the environment builder in its own file.
Fixed RuleDSL.lua globals.
Merge remote-tracking branch 'arcadepro/border'
Added an option to select the highlight texture.
Fixed a typo in Config.lua.
Renamed highlight textures to be more descriptive.

Fixes GH-45.
Tidied up allowed globals in rule snippets.