Add an option to mask variables for the linear stability problem

Issue/feature addressed

When masking regions in the linear stability analysis, the name of the selected region Unmask? is not intuitive. If a passive scalar presents, masking a certain variable is also useful. This feature is not supported yet.

Proposed solution

The function name Unmask? is changed into SelectEVCalcDomain?. The new function SelectEVCalcVariables is also added.

Implementation

Tests

A test has been added.

Notes

Please add any other information that could be useful for reviewers.

Checklist

• Functions and classes, or changes to them, are documented.
• User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Newly added files are correctly formatted.
• License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files). fix issue #310 (closed)