update Mpris2Plugin to py3

mpris2_support/__init__.py

@@ -1 +1 @@
-from mpris2_support import Mpris2Plugin
+from .mpris2_support import Mpris2Plugin

mpris2_support/manifest.ini

@@ -5,4 +5,4 @@ version: 0.3.1
 description: MPRIS2 support. Allows to update status message according to the music you're listening via the MPRIS2 D-Bus API.
 authors = Denis Fomin <fominde@gmail.com>
 homepage = http://trac-plugins.gajim.org/wiki/MprisSupportPlugin
-max_gajim_version: 0.15.9
+min_gajim_version: 0.15.10

mpris2_support/mpris2_support.py

@@ -1,7 +1,5 @@
 # -*- coding: utf-8 -*-
 
-import gtk
-import gobject
 
 from common import gajim
 from plugins import GajimPlugin