gsettings: Restructure gschema files

 * Add new list keys to track gsm (apn) and device (netusage) by address
 * Add plugin gschema as childs
 * Move org.blueman keys to org.blueman.general"
 * Add two keys to determine the dhcp handler.
gsettings: First attempt at porting to gsettings
gsettings: Fix schema id and path for network gschema.
gsettings: Correct key type and description for org.blueman.sdp gschema.
gsettings: Set a default height.