Overhaul of Kenwood D7 Driver

Removes dependency on kenwood_live, and implements a separate
radio class for D7 series radios.

Moves globals into the classes
- This allows finer control with subclassing

Clean up I/O
- Don't require a timeout after each command, speeding up access
  significantly
- Read all "garbage" bytes at the start rather than "just" 25

Add generic support for special channels
- Used for scan memories and call memories in the D7s

Makes settings easier to implement
- Data-driven description of settings with built-in support for
  bools, ints, strings, lists, and maps, which is enough for most
  settings
- Also supports custom classes for more complex settings, used for
  positions, DTMF memories, and programmable VFOs currently
- Allows for settings to depend on other settings
  Used for automatic simplex check and tone alert settings

Add full menu structure from the manuals.
- All settings listed in the manuals that can be controled via
  serial port are now exposed in Chirp