(bug 44744) notification with copyright warning in JavaScript UI

When going into edit mode on any part of an entity's UI, a new tooltip will appear,
displaying the Wiki's copyright warning which is also displayed when editing normal
(wikitext) pages.

The warning message will be put in a JS config var 'wbCopyrightWarning' in
EntityView::registerJsConfigVars. This is necessary because the message might be
generated in a more complicated way than just using a message. E.g. there is a hook
which allows for modifying the message. Also, the message is only available as
wikitext via EditPage::getCopyrightWarning. Since the frontend can't process
wikitext, we have to parse it first so 'wbCopyrightWarning' will hold HTML markup.

Change-Id: Ibc5cabfc0165d82e834fe195886a462f5ae9258d
NOTE: this is not yet working for 'add' buttons in jQuery.entityview UI elements.
Merge "(bug 44744) notification with copyright warning in JavaScript UI"