[aml] introduce guisettings overrides (v2)

This is useful for packagers as they can override menu defaults in as.xml
rather than patching xbmc code.

Usage example:

  <hidesettings>
    <setting>lookandfeel.soundskin</setting>
    <setting>videoplayer.rendermethod</setting>
  </hidesettings>
[aml] allow packager to provide a base guisettings.xml

place a guisettings.xml in system with any default values needed. These values
will only be used when user's guisettings.xml is generated. This way, packager
can set a default value (for ex, disable rss). Each profile will default to
this setting, but user's changes will take precedence.
[aml] Fix slow gui during fullscreen playback

If we're using bypass mode for playback, we aren't rendering ourselves, so
don't try to wait for render events.
[aml] frame-limit during fullscreen playback to avoid running at 100fps
[aml] add network Manager

Conflicts:
	xbmc/Application.cpp
[aml] fixed seeing usb keyboard/mouse devices that are inserted/removed after boot