Make the mirador config more easily alterable, Drupal-side.

[adam-vessey]

What does this Pull Request do?

Moves building up the "object" of Mirador viewer config PHP-side, so we can alter/adjust/augment it more easily, minimizing the size of the actual Javascript "integration" piece required.

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[jordandukart]

This looks fine here to me but given the in-flight work being undertook in the community I am hesitant to merge this prior to having more sets of eyes on this, primarily in regards to the roblib integration pull and the changing of the attached structure (albeit it's backwards compatability).

[alxp]

Just noticed that this was no longer marked as Draft.

I tested it and the plugins and everything still works as expected so this looks good.