Allow StyleAdapter to specify custom CSS plugins

@bug W-2419341@
@rev david.brady@
fix css error messages

@bug W-2419340@
@rev david.brady@
Add CSS check to prevent duplicate font-family in font-face tags

@rev david.brady@
@bug W-2419340@
update omakase version

+ StyleWriter can output comments
+ fix comments bugs
+ add font-feature-settings property
+ ability to dynamically annotate syntax units
+ add method to ErrorManager to get the name of the source

@bug W-2419341@
@rev byao@
@P4CL:9459981@
Merging origin/nathan/master-pending-adapter-css-plugins into master