Revert "Remove deprecated $wgCopyrightIcon"

This reverts commit 499aad5daa15b0eac8c6d5144f4e4216ee87e911.

[19:39:06] <MaxSem> Reedy, the wikimedia project button on every page is broken

Change-Id: I883c5598815fd17410022abe633f85cced94caba