gnome-power-manager icons should be part of theme

[Peter Hurley]

Now that gnome-power-manager is no longer part of the notification/indicator subsystem, it's status icon set should be moved into the 'gnome' icon theme.

The absence of appropriate icons is forcing devs to economize with poor substitutions. For example, the power plug-in of gnome-settings-daemon uses 'battery-*-symbolic' icon names preferentially now, which looks terrible. See attached screenshot.

[Peter Hurley (phurley)]

Cross-reference to corresponding bug #968769 in gnome-settings-daemon wrt using '*-symbolic' icon names.