Bug 957086 - patch 1 - nsIDataStore instead DataStore.jsm, r=ehsan

--HG--
rename : dom/datastore/DataStoreImpl.jsm => dom/datastore/DataStoreImpl.js
Bug 957086 - patch 2 - DataStoreService in C++, r=ehsan, r=bz, r=janv
Bug 957086 - patch 3 - DataStoreService in C++ OOP, r=janv