Split UserReporter JS and XML from mainmenu code and refactor it.
XML button duplication removal by bb in https://github.com/bb-bb/0ad/commit/62acfd74cb3efdb517db537bd4e62fa0ba6c304d
Write formatUserReportStatus in object-oriented style, refs irc discussion with Vladislav on 2018-08-10.
Add the two missing cases "proxy" and "waiting" from UserReport.cpp and reuse the "connecting to server" string.
No messages.json changes needed for the new directory, no string changes.