Bug 1018707 - Empty CustomCSS

Moved the default link styles to be first in the declaration.

Moved the .ignore-external class out of customCSS and into wiki.styl. I will remove it from customCSS when this change is live.
Merge pull request #2733 from stephaniehobson/BUG-1018707-empty-customcss

Bug 1018707 - Empty CustomCSS
bug 1065965 - Make disabled buttons less visible