Move test data out of inst

[rplzzz]

Right now, the test data gets installed along with the package. However, that data is only useful for running the tests and for use in the example vignettes. The price we pay for that is that the large files prevent us from distributing rgcam on CRAN, which we might want to do someday.

What if we took the test data out of the package install directory and instead gave it a permanent home on some appropriate archive? Then the tests and the vignettes could check for the test data in a local cache, and download it if it isn't there.

Alternatively, we could put the data in a separate package, which we could include in the suggests for rgcam and continue to distribute on github.

Thoughts?

[pralitp]

I don't mind moving it out (and maybe we could do it in such a way that we can share it with gcam_reader as well).

But we should just double check, I think we made defaults such that if you didn't specify a database (no connection nor path) it would give you the internal sample data. I don't think this is a feature we need to maintain but just something to watch out for when we do make changes. I think making this use case an error is totally appropriate.

[rplzzz]

Yes, I could live with making it an error not to specify a database. Having the default database was handy back when we were first developing the package, but at this point the test database is so limited that I can't imagine it's useful to anyone else.