Installer followup

See merge request !361

* Check if administrator rights are required
* Add INSTALL INSTRUCTIONS text file to root install folder in case the installer fails
* Add failsafes to uninstaller file deletion: check if name is a folder, and check for illegal chars
* Fixed parentheses breaking the installer by instead making exclamation marks do the breaking. Thanks Windows!

Add new Windows installer scripts

See merge request !356

Update debian packaging to work with Launchpad PPA

See merge request !350

Save sound toggles to config

See merge request !348

This reverts commit fd12e856.

Hide OpenGL loading screen

See merge request !349

FOF wall slope skewing backport

See merge request !341

Really I'm just making it return early if either of the parms are used.