PIM-2906: Merging all existing filter extensions into one agnostic filter extension
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
PIM-2906: Fix OrmSelector and typos
PIM-2906: Fix history grids
PIM-2902: Fix import/export grids
PIM-2902: Fix product associations grid
PIM-2902: fixing specs, addressing comments, typos and changelog
Merge pull request #1246 from akeneo/refactor/datagrid

Refactor datagrid stuff