It is part of the library - you'll find the Fiori controls under the sap.m (for "mobile") namespace in the API section. It's the "SplitApp" element that gives

It is part of the library - you'll find the Fiori controls under the sap.m (for "mobile") namespace in the API section. It's the "SplitApp" element that gives you the nice looking, responsive container (I was not able to find a good code sample right away).