Split STIPS data directory into run data and test data

[york-stsci]

Currently the STIPS data directory is ~330MB (~225MB compressed). Of this, ~80 MB is made up of test data and, as more tests are added, that fraction will increase. It probably makes sense to create a STIPS test data distribution that includes only the testing data, so that people using STIPS can decide to download either the bigger or the smaller file depending on whether they need the test data.