add Digi-Key + Adafruit PyCon 2019 board to builds

[ptorrone]

for circuitpython boards with different silk' on the board, let's add it as a build so it shows up on: https://circuitpython.org/downloads

add Digi-Key + Adafruit PyCon 2019 board to builds, can be a placeholder - images to follow soon and we'll also link to:
https://github.com/adafruit/PyCon2019

[tannewt]

Closing in favor of #1673 which is one issue for the tooling and can include initial boards to do.