MassMessage page input list improvements

by wctaiwan for Wikimedia

Currently, the MassMessage extension reads the list of pages to which a message should be delivered from a wikitext page containing a list of parser functions. This is not user friendly, and also technically undesirable since there is no enforced structure for the pages. This proposal seeks to implement a ContentHandler-based backend to replace the current system, and to create a usable frontend for managing the lists stored using the new backend.