Inform about moved code and prefer it over copied code

Summary:
Also reduce the memory usage a little bit (before increasing it again).

I use the same CSS class as for the copied code.

Test Plan: Parsed 100 diffs and checked about 10 of them - looks good.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Differential Revision: https://secure.phabricator.com/D2339