service: Added GATT server Heart Rate example

Added a simple example Heart Rate Service application that
demonstrates how to use the GATT server Binder APIs. The example
currently cannot respond to read/write requests or send
notifications as they are not supported in the API yet.

Bug: 24245347
Change-Id: Id10186a566559c9667adbd99b0484f2c90a422a0
4 files changed