service: Create a client library for applications

This CL creates the libbluetooth-client static library that external
code can link against to interact with the Bluetooth daemon using
Binder. To this end, all service/ code that is common to the client
library and the daemon itself have been moved to service/common/bluetooth
and service/common is exported in LOCAL_EXPORT_C_INCLUDE_DIRS.

bluetooth-cli and bt-example-hr-server have been update to demonstrate
how an app should use this library (using library includes).

Bug: 23169160
Change-Id: Ie6841bd6c48846eecec824ff1e80a9971385d1fc