Support for finger control without pen and interaction with pen

[marcobazzani]

This is a first working implementation for touchscreen without a pen (useful for scrolling with 2 fingers) it can be extended from here quite well it has been heavily copied from pimoroni/python-multitouch but the code wasn't in a usable form so I had to cut & paste it

[marcobazzani]

I also had to rollback some changes from the latest master because they didn't work and version 7.0.0 which is the one working and published on pypi is not present on this repository

[SBAPKat]

would be good to integrate a check for OS to not use this functionnality on windows, select.poll() isn't supported there and throws an error at launch.