Implemented SystemPropertyProvider
GB Settings need some system properties to adjust preferences.
Since GB Settings are running in user context it is necessary to obtain
properties from provider running in system context. Flow:

1) GB Settings send broadcast at startup asking for system properties
2) SystemPropertyProvider handles broadcast and packs system properties
into bundle which is then sent back to sender
3) GB Settings receive bundle and create local mSystemProperties
structure from bundle containing system properties. 
These can then be used during GB settings lifetime

There's a timeout implemented which handles a special case (e.g.
GB is not set as active module in Xposed Installer thus 
SystemPropertyProvider is not available to handle intent). 
In this case, attempt to read system properties is aborted after 5 
seconds and GB settings finished showing dialog with information 
to the user.