PIM-2906: Merging all existing sorter extensions into one agnostic sorter extension
PIM-2906: Merging all existing pager extensions into one agnostic pager extension
PIM-2906: removing datasource ODM adapter class from the datasource adapter resolver constructor (because this class is not registered in pure ORM)
PIM-2906: Introduction of an agnostic Datasource class. Introduction of pim_datasource_default, a default ORM datagrid.
PIM-2906: Introduction of pim_datasource_dual, a datasource that should be used for resources that are stored either in mongo or in orm (and which don't have a document manger).
PIM-2906: Listener to handle sorter configuration depending on the datasource and the storage driver