Allow creation of custom grouping of objects

[magnesj]

Use case

From a list of wells, allow the user to specify a subset of well. Give this collection a name, and show it in the Group section in the meta data. This concept can be extended to combine objects of other types also.

In a dialog used to define a custom group of wells, show selection of wells like this

Related code

See RimFileSummaryCase::createSummaryReaderInterfaceThreadSafe

Create a new class RifCustomSummaryGroup as sibling to RifCalculatedSummaryCurveReader. Add this reader to RifMultipleSummaryReaders
In this class, allow users to define custom subsets of wells, regions, completions, connections, etc. The mathematical operation to perform between the summary vectors is sum. Show these named custom subsets in addition to data coming from file.