Update twitter URL.

Twitter now uses https by default and you no longer need the hash bang (#!)
Makes themes resilient to stylesheets without trailing newlines.

Also deletes a bit of unused cruft from the dark theme.
Merge pull request #8594 from adobe/dangoor/8490-themes-trailing-newlines

Makes themes resilient to stylesheets without trailing newlines.
Merge pull request #8532 from wormeyman/patch-1

Update twitter URL.