Allow appending text to redirects from moved pages

Add message move-redirect-text, which is appended to redirects created by
page moves (empty by default). This could be used on enwiki to automatically
add {{R from move}} while still allowing non-admins to revert the move, for
example.

Change-Id: Ic2158897ce46177b695a7fb90c8ed3349df18bde
Merge "Allow appending text to redirects from moved pages"