Provide gup script that installs extension system-wide

[Lesik]

Hey,

for packaging this extension, it would be useful to have a gup script that installs system-wide.

I have created PR #195 for this, but I noticed that the resulting install has two problems:

• there are useless gup and .gup folders
• much more gravely, extension.js and prefs.js are symbolic links to outside of that directory, meaning the extension is broken outside of the build directory

Please fix these by providing a gup target that installs to the correct system path, respecting $PREFIX, and only contains data, lib, locale, extension.js, metadata.json, prefs.js and shellshape.pot, like the official zip you offer on GNOME's extension site.

[timbertson]

It's probably easier to make a plain install script rather than using gup - that way you can use:

gup --clean --metadata --force <target>

(doing that from inside a gup target would lead to sad times)

I've just moved the gup directory out of shellshape in b0d3d3f.

using cp -L (or --dereference) should fix the symlink issue?

There are a few other files that are excluded in zip.gup, but do they really matter? You could always build the zip then just extract to your destination it if you're worried about the extra files, since the zip is the thing that I care about as maintainer.