Issue #2618566 by xjm: "In core since" and the list of modules added to core does not work when providing data for both D7 and D8

Conflicts:
	upgrade_status.module

Issue #2172239 by xjm, webchick, chx, sun, Gábor Hojtsy: Flesh out list of modules that were moved to core in 8.x

Conflicts:
	upgrade_status.module

Add notification that the form submit worked so you don't drive yourself completely insane re-submitting the form 50 times thinking you're doing something wrong. Ahem. Patching for a friend. ;)

Also moving upgrade_status_core_version_form() and upgrade_status_core_version_form_submit() to upgrade_status.module for the same reason.

Moving upgrade_status_moved_into_core() into the .module file to make it cleaner to see what's forked vs. not in update.compare.inc.