ADD: matchesregex() to the visibility expressions

This adds the function ```matchesregex(INFO_LABEL, STRING, [BOOL=false])``` to the ```<visiblity></visibility``` stuff of the skinning engine.

BOOL= if true, the regex matching will be case insensitive

Befor you ask why? This feature was requested in this PR #1654 by @bstrdsmkr.
This feature seemed standalone enough so I decided to make it a seperate PR