Updated mediawiki/extensions
Project: mediawiki/extensions/MassMessage  bbc1921d0ba1f9a36acbe1205eb747a2c0aae1cf

Only have the CSS apply inside "mw-massmessage-form"

To match all the other form keys, a "mw-" prefix was added.

Change-Id: Ia79f569f85b27502914000f9c526d3589138c1ff