gsettings: Restructure gschema files

 * Add new list keys to track gsm (apn) and device (netusage) by address.
 * Add plugin gschemas as childs.
 * Move org.blueman keys to org.blueman.general".
 * Add two keys to determine the dhcp handler.
 * Add plugin-list key to org.blueman.general.
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.
gsettings: Fix some of my sillyness in efb349f586d228b4f61c7292eea30b1f9e2ebb12