Suppress controls UI updates when hidden
Suppress controls UI updates when hidden

This makes the demo app run more efficiently and may save battery on
devices.

Closes #749

Change-Id: I735cde417c04cf8c2e7d93944d1c80a0298a7111

vimond/shaka-player,Ross-cz/shaka-player,shaka-project/shaka-player,TheModMaker/shaka-player,Ross-cz/shaka-player,indiereign/shaka-player,brightcove/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,russitto/shaka-player,shaka-project/shaka-player,indiereign/shaka-player,Ross-cz/shaka-player,vimond/shaka-player,tvoli/shaka-player,tvoli/shaka-player,russitto/shaka-player,shaka-project/shaka-player,russitto/shaka-player,brightcove/shaka-player,shaka-project/shaka-player,TheModMaker/shaka-player,TheModMaker/shaka-player,brightcove/shaka-player,tvoli/shaka-player,vimond/shaka-player,indiereign/shaka-player