Relicense the Mir client plugin

Use the standard Qt Project template, while retaining
the copyright. This adds Qt Commercial and GPL version 2
in addition to LGPL version 3.

Change-Id: Ib4d6732f843b0bf3f3bb9563cb4b3e576967f1cd
Reviewed-by: Gerry Boland <gerry.boland@canonical.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>