Extension:MassMessage/Page input list improvements/Progress reports

Current project status

 * The new backend is functional and delivery works, along with basic list creation / editing UI
 * Work starting on a more user-friendly UI
 * Currently working on an API the UI can use to add / delete targets from delivery lists
 * To be worked on in ContentHandler code:
 * Caching
 * Tests
 * Prettier diff
 * Ability to edit old revisions

Progress reports

 * Community bonding report
 * /May
 * /June

Week of June 30

 * June 30: Worked on code refactoring, submitted as ; submitted.
 * July 1: Discussed and planned user interface for basic list editing and related API with mentors.
 * July 2-July 3: Submitted ; worked on API.
 * July 5-July 6: Worked on API and reducing code duplication (it turns out that the API would do a lot of what Special:EditMassMessageList already does); submitted.