Added some functions to GeoNetworkRecord and some refactoring to enable ActiveGeoNetworkRecordStore to more easily add layers to layer store.
Renamed DownloadList to DownloadDataView (mainly to indicate that it is a view class rather than a model class).
Refactored download data view template in to own class for clarity.
It's now possible to pass a callback in to the layer store addUsing* functions.
This will be called just after a layer is added, with the newly adder layer record.  This is useful for callers who need to know the record which was added as a result of their call in the LayerStore (e.g. the ActiveGeoNetworkRecordStore).