Add new Action ToggleCECDevice() to switch state of playing device via a CEC peripheral

As continuation of https://github.com/xbmc/xbmc/pull/2012, which left an unmerged commit, this is to add the ToggleCECDevice() action, which can be mapped to a remote/keyboard and can be called as a xbmc builtin.

I have renamed all the functions to ToggleCECDevice(), but the one within PeripheralCecAdapter, which I called ToggleDevice(). I think this is in line with the rest of xbmc's code.