tar_em_up.sh: Fix the ARM nw.js package names and versions.

This brings the ARM nw.js versions in the tar_em_up.sh script up to the same versions that we use in the OBS builds, and makes sure that the right packages are downloaded and extracted properly, without any manual intervention, on both armv7l/armhf and aarch64/arm64 systems when building locally with make. Tested on a Raspberry Pi 4, with both the regular (32 bit) Raspbian Buster and the latest 64 bit beta version of Raspbian Buster available here: https://downloads.raspberrypi.org/raspios_arm64/images/raspios_arm64-2021-04-09/

Note that, in particular, this updates the (ancient) 0.17.6 nw.js version that we still had in the script to the 0.27.6 version which has been used in all our OBS builds for quite some time now. It also adds Maurits Lamers' arch64 nw.js 0.23.7 build that we added recently, and fixes the upstream URL so that it correctly points to https://github.com/LeonardLaszlo/nw.js-armv7-binaries/releases/download/ for the ARM packages now.

This doesn't change any of the other nw.js package URLs or versions, so building on the other platforms (x86 Linux, Mac, Windows) works the same as before.