InstallFonts.ps1: Add ability to install fonts per-user without admin rights. Fixed version.

[electr1cBugaloo]

This PR only modifiies InstallFonts.ps1. There are 2 basic changes:

add the ability to install fonts without admin rights for the current user only. Requires win 10 build 17044 which we check for.
Somewhat restructure/try to improve the code but try to keep the same basic structure which you used in your branch.

Please note I unfortunately somewhat messed up my git commits, so there are less small commits and only two or three larger commits. Sorry about that.