Remove the need for image files in tests.

This PR does away with needing actual images to do the class and parse tests. This means that instead of needing 1.6M of test data we now just need 928K. There might be even more ways of reducing data/timestream-good-images but it might be a bit more work that what I have done in the past week.

Please consider this for merging.
I believe that there *has* to be a tab at the start of these strings, and I can't tell from github if it's been preserved.