Add 'Contact Wikipedia' footer link on test/test2

Adds a configuration variable, '$wmgUseFooterContactLink' (default false). When
true, adds a 'Contact Wikipedia' link to page footer. Enabled for test and
test2wikis, with an eye toward enabling on enwiki.

Bug: 46392
Change-Id: Iab1f5f52742e899fc40028bb5993c024241a87bd