Load corresponding grid or summary data for an ensemble

[RezaeiDoust]

If a user has already loaded a full/subset of ensemble of summary data, it should be possible to load the same subset of grid models by simply selecting whether it is "grid case group" or "ensemble".

The reverse direction is also valid. if a user has a grid case group and decides to load the corresponding summary data it should be done with more ease.

this could enable making any subset based on conditions, correlation x-plot and ... and analyzing both summary and grid data