Add a possibility to merge binaries using esptool.py

[jnthas]

Useful information: it's possible to merge all binaries in a single one using merge_bin command like described here: https://docs.espressif.com/projects/esptool/en/latest/esp32/esptool/basic-commands.html#merge-binaries-for-flashing-merge-bin

I create a simple script to merge and flash before I push changes https://github.com/jnthas/improv-wifi-demo/blob/main/firmware/merge-and-flash.sh

[tyeth]

Mergebin in JS form: https://github.com/adafruit/esptool-mergebin-js