Allow Saving to Audience Library for Combined Audiences

Description - Allow for more flexibility of saving combined audiences to the Audience Library. These should include: audiences that include a previously saved Audience Library audience combined with an AAM audience. Also, an AAM audience, or previously saved Audience Library audience, that is excluded from 'all visitors'. 

Why is this feature important to you - We reuse several audiences repeatedly and it would save time and minimize error if these combined audiences could be saved to the Audience Library and just referenced as one audience rather than having to rebuild it each time.

How would you like the feature to work - Should work the same as creating audiences and saving them to the Audience Library today.

Current Behaviour - Currently, there is no option to save a combined audience to the Audience Library. The radio button is grayed out. Those audiences can only be saved to Activity-Only