AJAXify watchlist editor

AJAXify watchlist editor

This patch makes the watchlist editor to use pagination. That would
avoid old browsers crashing (bug 20483).
Patch also add some AJAX operations to the editor, for example to remove
items from watchlist (bug 32151).

The AJAX support is an ALTERNATIVE to the form based method, to keep
support for non javascript users.

This change contains a required change in the API for watch operation,
to allow batch operation, by support titles parameter. The old title
(single page) parameter is still used to keep backward compatibility.

Change-Id: I1d8c66db9ba6456858ef655397935a2b3a421632