Added data store backend. (#17)

* Added data store backend.
* Add NFS implementation for Kubernetes.
* Added S3 data store implementation.
* Addressed review comments.

rl_coach/data_stores/data_store.py

@@ -0,0 +1,26 @@
+
+
+class DataStoreParameters(object):
+    def __init__(self, store_type, orchestrator_type, orchestrator_params):
+        self.store_type = store_type
+        self.orchestrator_type = orchestrator_type
+        self.orchestrator_params = orchestrator_params
+
+class DataStore(object):
+    def __init__(self, params: DataStoreParameters):
+        pass
+
+    def deploy(self) -> bool:
+        pass
+
+    def get_info(self):
+        pass
+
+    def undeploy(self) -> bool:
+        pass
+
+    def save_to_store(self):
+        pass
+
+    def load_from_store(self):
+        pass