Fix file locations and packaging for initial rPi3 version

[tve]

This PR contains several separate commits that are necessary to perform a complete image build using sensorgnome-build resulting in a functional sdcard image. Specifically:

• the FAT32 data partition is now at /data but some of the code in this repo didn't get updated.
• it is unclear which version of socket.io was used by the code, but the API used works neither with v2, v3, or v4, thus the code got updated to work with the current v4 version of socket.io
• the machine ID was being stored in /etc/beaglebone_id, but cripts in sensorgnome_support wrote it into /etc/rpi_id, which caused problems, this is resolved by always storing the ID in /etc/sensorgnome_id

Note that the changes above make it that the software cannot be installed into older systems, the new image layout is assumed. Unless old beaglebones need to be updated and the new image cannot be built for BBB this should not be a problem.