(WIP) optional use of esptool.py for flashing

[d-a-v]

Untested in all situations

This is an option.

• tested with linux and wemos d1 mini
• original esptool is still used to generate the image (it sets at least flash freq and flash mode)
• erase command not treated (yet)
• reset method not treated (yet) (working with d1 which uses nodemcu method, esptool.py by default? triggers DTR)

How to try:

• run get.py to download esptool.py.
• run tools/board.txt.py --esptoolpy --allgen
• restart IDE

How to get back to default:

• run tools/board.txt.py --allgen
• restart IDE

(the big changes in boards.txt.py is only the macros variable moved from global to all_boards() function because it uses now the new esptool variable)

[d-a-v]

closed in favor of #5635 which is running very well