WIP - Enable OTA

[earlephilhower]

Insert a stub app that will check for work to be done, and if so do it. If no work to be done, jump to original app.

Uploads, including password protected, work through the IDE now.

DONE:

• [X] Replace boot.o with OTA.o (which will include the appropriate boot2)
• [X] Define area to store work to be done, format of work block
• [X] Add in R-O LittleFS code
• [X] Add in UZLIB compression lib
• [X] After upload erase work block and reboot
• [X] Make constants less magic in OTA code
• [X] Add simple file example
• [X] Add compressed example
• [X] Add mDNS for Arduino IDE OTA support
• [X] Add ArduinoOTA class on core and uploader Python script
• [X] Add checksum
• [X] Add Updater() to allow signed updates

TODO:

• [ ] Add WiFi example
• [ ] Add mDNS docs, including new background mode
• [ ] Add docs