Added support for multiple processes on capable microcontrollers

[JonathanSafer]

Description of Problem

All of our code currently assumes it is running in a single thread. In order to support multi-core microcontrollers, we'll need to modify each component to function in both a single and multi-thread context.

Solution

• created a generic RocketController interface with common functions to be used in main.ino
• created source files for single and dual core contexts to link with the controller header
• shifted around certain libraries to facilitate correct linking
• moved SD card backup calls to the 2nd core in the dual core implementation
• labelled state as volatile so it can be used asynchronously

Testing

• untested :/