Floating Command Window

* **Description**: Silent, borderless window that acts as text field for the commands.
* **Acceptance Criteria**:
    * Must exist a `CommandUI.mm`
    * Must init an `NSWindow` with `NSWindowStyleMaskBorderless`
    * Must set level to `kCGScreenSaverWindowLevel`
    * Must ensure it does not steal focus when shown (or immediately returns it)