Raspberry Pi Pico support and organizational changes

[JonathanSafer]

Description of Problem

These changes encompass everything that was needed to support a new flight computer: Birdbrain. Birdbrain is roughly derived from Catalyst-2, but includes several hardware changes, including a new microcontroller, IMU, radio, SD card module and pyro channels.

Notable Changes

• replaced references to Catalyst-2 with the new software name: Stimulant
• Added a sensors directory with interfaces for some of the sensors
• added source code for LSMDSOX
• replaced settings.h with config.h and added a config for each supported flight computer (Catalyst-2 and Birdbrain)
• added build flags in platformio.ini to link source code
• modified unit tests to "work" with the new architecture (further modification will be needed)

Testing

• Flight tested with successful main parachute deploy (triggered by lack of drogue failsafe) (Birdbrain)
• Ground "throw" tests (Birdbrain)

closes #15