Refactor/improve ensemble select dialog

[jorgenherje]

Refactor/improve the ensemble select dialog component.

• Allow creating delta ensembles compare and reference ensembles not among the "Select Ensembles".
• Consider pairing an ensemble and a RealizationFilter s.t. an application can have multiple instances of an ensemble with realization filters - allowing comparing the ensemble with various filters in a module: Have RegularEnsemble/DeltaEnsemble and corresponding RealizationFilter as an ensemble entity? #828
• ...
• Add more...

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Suggested changes/improvements:

• Make the "navigator" part in the dialog a separate component, s.t. it will become a dialog/selector or similar, which will appear when one wants to add an ensemble. The same component can then be used when creating delta ensembles, instead of a dropdown?
  

• For delta ensembles: Create a component which is a sort of dropdown, used to select the compare and reference ensemble. The dropdown can then list the "Selected Ensembles" for quick access, and a last option "Select another ensemble..." which opens the reusable component mentioned in the previous bulletin.

[HansKallekleiv]

Having the navigator / "ensemble browser" as a separate component is a good idea.
We should also add more information and make it easier to find ensembles, e.g.:

• Sort cases by date
• Filter cases (ensembles) on which simulation run was used (experiment, smoother, etc)
• Filter on available datatypes / contents in a case. E.g. summary, surface, inplace
• Display case/ensemble metadata. This might be just showing the description metadata string somewhere.
• Link to case in Sumo?

Future possibilities:

• Select subset / working set of data for a case upfront?
• Populate a cache in background?