Refactor stores into own package

Dockerfile

api/api_test.toml

api/initialise_test.go

controller.go

northbound/server/csbi.go

northbound/server/nbi.go

northbound/server/pnd.go

northbound/server/pnd_test.go

nucleus/initialise_test.go

nucleus/principalNetworkDomain.go

nucleus/principalNetworkDomain_test.go

nucleus/store.go

nucleus/store_test.go

store/changeStores.go

store/change_store_test.go

store/deviceStore.go

store/device_store_test.go

store/genericStore.go

store/generic_store_test.go

store/initialise_test.go