README: add kernel modules documentation reference

Use proto2 syntax

use python3

Add xdg menu category for anbox apps

explicitly use python3 in script, docker and snapcraft

platform/sdl: Disable mouse event emulation for touch input

SDL 2.0.10 introduced mouse event emulation for touch input.
However, Anbox already handles touch events by itself, so this just
results in duplicated events and erroneous input when using Anbox
with a touch screen (for instance, on the Librem 5).

Signed-off-by: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>

restore travis and Github CI behavior

More sensors support

do not automatically hard reset git tree on build