Resolve L2SS-1438 "Unify abstract hierarchy"

README.md

tangostationcontrol/VERSION

...fault/devices/base_device_classes/test_power_hierarchy.py

...gostationcontrol/devices/base_device_classes/hierarchy.py

...oncontrol/devices/base_device_classes/hierarchy_device.py

...tationcontrol/devices/base_device_classes/lofar_device.py

...ioncontrol/devices/base_device_classes/power_hierarchy.py

...ioncontrol/tangostationcontrol/devices/station_manager.py

...ontrol/test/devices/base_device_classes/test_hierarchy.py

...test/devices/base_device_classes/test_hierarchy_device.py