Add support for ESP32 board

[Jinnie]

Currently only ESP8266 is supported. ESP32 is a newer chip and would be nice to get support for it too.
Not sure if it can be in the same codebase, or we need a separate branch. I would prefer keeping in the same branch if possible, but this will require duplicating different libraries. At least:

• servo control
• web connector

This may not even be possible. I have poor CPP experience, so I'd appreciate any comments about how we can either abstract the board or have 2 branches for the boards which will share the board non-specific code some way.