[bugfix-1.1.x] Platformio - automate build & environment selection

[Bob-the-Kuhn]

This is the bugfix-1.1.x version of PR #10503. See that PR for details.

The changes to implement this feature are:

• copy auto_build.py from 2.0.x into bugfix-1.1.x
• copy process-palette.json from 2.0.x into bugfix-1.1.x
• copy the comments in pins.h from 2.0.x into bugfix-1.1.x
• change platformio.ini to treat the teensy20 boards as is done in 2.0.x. This consists of replacing the Brainwave Pro, Printrboard and Printrboard rev F environments with one called teensy20. The only real change is that the board identifying flags were dropped. These flags were not used.

This has been tested on a 2560 board and a 1284 board.

[thinkyhead]

Easiest way to fix it up is to use git rebase -i and just "drop" the two extra commits. No need to move to a whole new fork.

[thinkyhead]

This will soon pass Travis CI, no doubt: 382aa96