Fix 691: unzip files using a stream to reduce RAM load

[davidmurray]

In Transition, we zip and unzip files for GTFS exporting and importing.
I could not find a package that allowed unzipping using a stream but also allow zipping files. This PR uses https://github.com/antelle/node-stream-zip, which only allows unzipping. We must therefore keep our current dependency on JSZip.

The options are as follows:

1. Accept this PR which unzips using a stream, but adds an extra package dependency
2. Spend time writing our own zip/unzip code (or find an existing library to extend/improve)
3. Drop both packages (JSZip and node-stream-zip) and instead ask users to install the unix zip utility on their workstations (it is preinstalled on macOS and probably most linux distros anyway)

[greenscientist]

I'm fine with this option 1. Maintaining our own code or having to rely on a system zip, which might be different depending on the OSes all sounds more complicated.

[greenscientist]

This looks good to me.

(will need a rebase to re-ruin the test)

[tahini]

Please rebase this PR for the CI to pass, but looks good