Show warning message instead of TestsDialogWindow when no methods/classes available

[volivan239]

Description

If user launches "Create tests with UTBot" on a class that has no methods (or no overriden methods), plugin shows a dialog with empty list of methods and disabled "OK" button which seems odd.

Expected behavior

Show a warning/error message stating that there are no available methods for test generation.

Potential alternatives

Other ways to clearly inform that there are no methods/classes available for testing.

[volivan239]

It was decided that in above example we should just disable action and do not show anything; but we should show info message in case we create tests for package and no methods were found for listed classes