Deploy Flow, Echo and Thanks extensions

Source code will be available, but extensions won't be enabled.

So this change is no op for MediaWiki live code.

Summary: Ref T1374

Test Plan: ls /srv/mediawiki/extensions

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1374

Differential Revision: https://devcentral.nasqueron.org/D1516