Inter board communications, etc.
1. Implement handshaking between rear and front boards
2. Remove RTC from front board
3. Juggle interior board thread priorities
4. Add check for external board command length overflow
5. Fix sign error in IP address lookup
6. Silence some compiler warnings on interior board build
7. Double buffer serial command handling
8. Fix LED control from interior board
9. Fix some image transfer content length book keeping