Windows Installer : Python3 + 64bit

Upgrade of windows installer build system:
- revisions.txt supports "local" to point to local working directories
- msys2 ucrt64 64b runtine
- use requirements.txt
- most python packages from msys2 repo
- still use pip/wine for other python packages
- some cleanup in Makfile code, removing dead code
- CANopen, Modbus and OPC-UA not included... to be continued.

# Snap distribution

main_target: Snap

tar_opts=--absolute-names --exclude=.hg --exclude=.git --exclude=.*.pyc --exclude=.*.swp

Snap: snap_built
snap_built: all_sources revisions.txt
	tar -C $(src) $(tar_opts) -c snap | tar -C sources -x
	cp revisions.txt sources
	cd sources;  snapcraft --debug 
	touch $@