Add slider to control video quality

This reverts commit 953969acc04e8ec1f9731dce770d187599e37e6d.
It also adds a checkbutton below the slider which enables
automatic video quality adjustment (and is on by default).

The slider now has a range of 0 to 100 and sets both the bitrate
and quality parameter of each codec by getting the min and max
values of both and scaling the set value.

Change-Id: I307e541c6e30c432ab5452bba2af9c2f069d79d9
Tuleap: #215
diff --git a/pixmaps/pixmaps.gresource.xml b/pixmaps/pixmaps.gresource.xml
index 23c4b62..a143e94 100644
--- a/pixmaps/pixmaps.gresource.xml
+++ b/pixmaps/pixmaps.gresource.xml
@@ -16,5 +16,6 @@
 	<file alias="mute_video">ic_videocam_off_black_24px.svg</file>
 	<file alias="pause">ic_pause_black_24px.svg</file>
 	<file alias="end">ic_clear_black_24px.svg</file>
+	<file alias="quality">ic_high_quality_black_24px.svg</file>
   </gresource>
 </gresources>