Session and SessionCollection

New Redfish-Core nodes added (removed from redfish_v1.hpp) - Session
and SessionCollection. Tested manually on x86 VM and Wolfpass Platform.
Behavior almost identical to what was before - differences:
- SessionCollection - now only returns TIMEOUT presistence sessions, not SINGLE
- Aquiring sessions from session storage now applies timeouts

Change-Id: I68bf4fa7fa1c8371216a7d4daa30bbfb653cfa72
Signed-off-by: Kowalski, Kamil <kamil.kowalski@intel.com>
diff --git a/include/session_storage_singleton.hpp b/include/session_storage_singleton.hpp
new file mode 100644
index 0000000..6ff8a0e
--- /dev/null
+++ b/include/session_storage_singleton.hpp
@@ -0,0 +1,10 @@
+#pragma once
+#include "sessions.hpp"
+
+namespace crow {
+namespace PersistentData {
+
+static std::shared_ptr<SessionStore> session_store;
+
+}  // namespace PersistentData
+}  // namespace crow