Enable more customization for bootstrap-treeview

[svenevs]

The bootstrap-treeview library provides significantly more customization than is currently exposed.

I got things setup far enough to satisfy my own needs, are there specific features people want that they cannot access?

Global configurations are likely the only ones that can be supported. Or at least node-level configurations in the json data would be significantly more challenging to both implement, as well as specify in exhale_args.

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There currently exist quite a few pass-through options, but it seems likely people would potentially want more. This issue will basically remain open quasi-indefinitely.