arduino: Add RPC memory allocation commands
duinocube: Split various subsystems into separate classes

Split DuinoCube class into the following classes:

DuinoCube - manages SPI and sets up Core and System classes.
DuinoCubeCore - controls the Core shield (video/audio).
DuinoCubeSystem - manages System shield shared memory and logic. Sets up
                  subsystems (File/RPC)
DuinoCubeFile - File access layer.  Depends on DuinoCubeRPC.
DuinoCubeRPC - RPC client layer.  Depends on DuinoCubeSystem.

The examples have been updated as well.