2_add_power_mgmt_svc: Added I2C driver to configuation
2_add_power_mgmt_svc: Added the source and header files of the service implementation
2_add_power_mgmt_svc: Add a whole lot of other shit which I'm not sure is required for build
2_add_power_mgmt_svc: Added implementation of power management service
Merge branch 'feature/2_add_power_mgmt_svc' into develop
4_add_rx_to_btstack: Added untested implementation

Directly ported over codebase from original project. Compiles but
untested.

Fix doxygen comment for issue #3
Hotfix: Explicitly declared UART mode as blocking (probably were before)