Move GC iframe css into code

Copied from https://wikimediafoundation.org/wiki/MediaWiki:GlobalCollect.css
and merged the RTL changes in by hand.

Should be included from the GC skin like so:
https://payments.wikimedia.org/load.php?debug=false&lang=en&modules=gc.iframe&only=styles
and for RTL,
https://payments.wikimedia.org/load.php?debug=false&lang=ar&modules=gc.iframe&only=styles

Change-Id: I8f0588007804d6260dac9f739e5dcb1734c0199c
Merge "Move GC iframe css into code"