Lots of work refactoring code.

[f34rdotcom]

• [X] Put STSDK and TWILIO into modules that can be enabled / disabled in stsdkconfig
• [X] Subscriber model now supports multiple subscribers for AD2 events.
• [X] Added Firmware AD2 event.
• [X] Switch everything to C++
• [X] Added OTA update and version CLI commands
• [X] Started adding STRINGs to EVENTs lookups for HUMAN readable event strings.