Adds the three CSS3 attribute selectors.
During this the internal naming of the existing attribute-selectors have
been changed to be more clear, and the dash-matching has been fixed to
not just be beginsWith.
A non-breaking space have also been removed from the CSS.
Change-Id: Ia4db4a5a19e3ceee8c3c8a4b744149edd1d32bdc
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>