Use REACT for Explorer

[lrennels]

Now that we have added components we want to allow things like a tree-view dive into composite components. Motivated by this, we have decided to convert the framework over to REACT. To-do items include converting the current framework over and getting that to work, followed by adding component viewing etc.

Currently being handled here: #719

[davidanthoff]

Here are the UI libraries that I've heard from:

• https://developer.microsoft.com/en-us/fluentui#/get-started/web - on this page see Motion --> Drill In, also I think has _Tree` component, found the docs a little confusing at first pass
• https://material-ui.com/ - has good docs and TreeView support
• https://semantic-ui.com/
• https://react-bootstrap.github.io/

I guess the first thing to check is which of these have some sort of support for the kind of hierarchical tree view thing that we need?