This PR is a WIP aiming toward a "steel thread" blinky demo showing new structure for the project.

• Move svd2rusty into an svdgen crate inside this project
• Make a crate that has all of the stm32f405 specifics for that firmware
• Call svdgen from build.rs
• Port hal logic into for clock and GPIO
• Add app logic that expects a button and an LED via a Board trait
• Implement the Board trait using the hal GPIO tools
• Port the main logic from the ui crate to instantiate the app and create a coherent firmware