Fix power menu not updated on select of a powered off player

Unknown power status was confused with power off, so we use a nullable
boolean to hold the power status of the player.

Signed-off-by: Kurt Aaholst <kaaholst@gmail.com>
Add power controls to player list

Players can be turned on/off from the player list.

Also disabled player selection from the player list, as this is now
handled by the player dropdown in the action bar.
Update player icons and add icon for squeezeplayer

also removed some unused icons
Do not reorder players if we already have them
Rename player

available as on option in the player list context menu
Move onRestoreInstanceState to onCreate

As onRestoreInstance was called after onCreateDialog in the dialog,
which needs the activity state.

Yet another fragment issue :-(
Substitute View.setlpha with Drawable.setAlpha

to support API levels before 11
Support player sleep

Also use alpha animaion instead of Drawable.setAlpha, as the alpha
value applied to all instances of an image resource
Control volume in player list
Player list discover player changes

i.e. when players connects or disconnects from the SqueezeboxServer.

The players changed callback has been moved to its own callback type,
so interested parties can subscribe to events.