Surround edit notices with appropriate classes

Surround edit notices with appropriate classes

This commit adds a <div> around edit notices with relevant classes to aid in the
creation of user scripts, following an earlier change (bug 30959) for
edit intros.

It adds an .mw-editnotice class to each edit notice, and because classes are fairly
cheap, a second mirroring the edit notice's message key, and a third depending
on the edit notice type:
	.mw-editnotice-namespace	for a namespace-wide edit notice
	.mw-editnotice-base		for a edit notice for the subpage's base page
	.mw-editnotice-page		for an edit notice set explicitly for the page

Classes are sanitized where required.

Bug: 68749
Change-Id: Idf44f2a344d64893f799286914bda3f8d4aff6bf