Currently, when you have multiple contexts in an extension you can select the context in the fields manager, but not in the fields groups manager.
Since field groups now use the full context instead of just the extension, we need a way to select the correct context.
Summary of Changes
Adds the context selector to the fields groups similar to how it is in the fields manager.
Testing Instructions
Go to com_contact, create a field group and try to assign that group to a field of the context "Mail". The newly created group will only be available for fields of the context "Contact".
Apply this PR and try again, now changing the context to "Mail" prior of creating the field group. It should work now.
Sometimes I think you can read my mind? .