Systematic testing of all packages in the GAP distro

[fingolfin]

We should test all packages in the GAP package distribution within GAP.jl. That means running TestPackage("PKGNAME");.

I am sure this will reveal a bunch of issues. For starters, we may need to add a GAP.Packages.build() command so we can use the bundled version of those packages without installing newer ones (without any network access in fact).

Some of this my be rendered moot by switching to GAP_pkg_* wrapper packages (but I view this issue as orthogonal to that. I.e. even if we had GAP_pkg_* wrappers in place right now, I'd still would want to run their tests -- it just would be a tad easier to do so because I would not have to worry about building them).

On the long run, these tests could be automated by CI. E.g. perhaps in the https://github.com/oscar-system/GAP_pkg repository there could be a CI job for each package (with a few disabled).

Of course a few things never will work in their current form (e.g. I have no hopes for xgap and hence itc). That's fine. But yesterday I tried to install and run nq and anupq and embarrassingly ended up running headlong into issue #1064.