UI: Settle on first officially supported UI

[mormj]

There are multiple options options floating around to solve two distinct but related problems that GRC solved for GR3:

1. A block based canvas to connect and configure the flowgraph
2. Runtime visualization of graphical blocks (like qt gui blocks)

Some of the options for (1) include:

• GR4 Studio (https://github.com/altiolabs/gr4-studio)
• CyberEther (https://github.com/luigifcruz/CyberEther)
• Rework GRC
• imgui / gr-digitizer based