Rendering customization window

This is a very basic customization modal. It's simply a window that pops up over the page with some options to change the final rendering. I've applied it to the `tree_viewer` *only*. Right now, it only changes the rendering of the tree between static and dynamic view. 

Two things:
1. I've created a generic modal object that can be populated to fit various visualization representations
2. Each visualization can have an `Options` object that holds specific customizations to that type of visualization. 

There is still tons of work to be done. I'm opening this PR early to show my idea here. It's not ready to be merged.