GPII-545: Adding the new GPII usb user listener code

The new GPII usb user listener is now a standalone application.
It covers all the workflow that we need by itself, from detecting the
device to trigger the login/logout processes.

Since the user listener now is standalone, it should be installed in any
well-known 'bin' folder by the system, this is, a 'bin' folder which is
included into $PATH environment variable.

Also, we are providing a '.desktop' file for the users to run it easily
in the same way they launch any other application from the system.
GPII-545: Updating build.sh according to the new GPII usb user listener
GPII-545: Removing old GPII usb user listener-related stuff
GPII-545: Updating README according to the new GPII usb user listener

Removing tests/.gpii-user-token.txt. I don't think much people is using
this now since '123' N&P set doesn't exist anymore in
testData/preferences folder of the universal repo and nobody noticed it.
GPII-545: Renaming README file as README.md
Merge remote-tracking branch 'javihernandez/GPII-545'