SharePoint configuration service

New configuration service that allows to parametrize:
* minimalLoadSharePointInfraestructure (default true):  SharePointReady
function only load sp.js
* force15LayoutsDirectory: (default false): when the framework load
SharePoint scripts from _layouts directory, forces to load from
_layouts/15/… instead of SP.Utilities.Utility.getLayoutsPageUrl(…).
Over SharePoint 2013 platform with migrated sites from 2010 but without
UI experience, certain javascript files are not in the _layouts/14/…
directory, and you need to force this flag.