Add ability to group requests in folders

[codymullins]

MudBlazor supports nested lists and tree views. We should be able to utilize these components to be able to create folders for our requests.

This will require both UI changes and data structure changes.

UI

• Add new button/button group with the existing "add request" button for folder creation
• Add ability to move request into a folder or out of a folder
• Add ability to delete folder + contents
• Add warning for deleting folder with contents
• TBD

Data structure

• Add support for folder location on the SpacetimeRequest
• TBD