Change logfiles file format to zip

[peteruithoven]

Currently the logfiles get's exported in a .tgz file format. Recently github allows adding files to issues, but it only allows ZIP files. Could we export the logfiles in zip format?

[woutgg]

The zip program (under Utilities/Compression in menuconfig) is not installed by default, but we could do so, unless it would take up too much space.