Fix edit link for messages in $wgForceUIMsgAsContentMsg

Fix edit link for messages in $wgForceUIMsgAsContentMsg

Some special pages or actions have a link for users with editinterface
rights to edit the message used in scroll down menu.
When the message is parsed for the scroll down menu the config
$wgForceUIMsgAsContentMsg is used, but that was not used for the edit
link.

Add a new function Message::getTitle and use it in all places in core.

Most benefit will have the edit link for MediaWiki:Licenses on
Special:Upload, because commons.wikimedia.org has that message in
$wgForceUIMsgAsContentMsg.

Change-Id: Ib800b9adcc9ae88ef53228b66838bf61d2065f0f