hide static links for any system tiddlers prefixed "$:/"

also added underlined format to make it at least stand out a little,
even if not a link
also hide shadows, no underlined url
changed system tiddler filter check
Merge pull request #1133 from tobibeer/no-static-links-for-system-tiddlers

#1129 — hide static and github links for any system tiddlers prefixed "$:/" on tw.com