bluetooth,treewide: Clean up BlueZ macro defines, use DBUS_ macros in more places

BlueZ macros are currently (re)defined in many places which is confusing: move them all to bluez5-util.h where they are accessible to all. Also replace some string literals with existing or new defines for consistency.

At the same time DBus string literals couldn't be left behind, and have also been replaced with their preprocessor-defined countrparts; in the entire tree for consistency instead of just Bluetooth code. Let me know if that's okay and hopefully not too spammy/unnecessary?