Support for packages with multiple components

Some addon folders appear to contain multiple liveries inside them, even though they are treated as a single addon from a PERFLIGHT perspective.

• Make the addon data model more "multiple" aware?

• Offer users the choice of selecting from other promo/hero images which exist inside "multiple" packages?

• Display some sort of "multi" pill in the UI?

The most obvious example is PMDG (777-200ER shown here)

Or 738 shown here: