The integration test checks that moving in image coordinates fails
before the CSM thing is calibrated.
Unfortunately, it is missing the `y` argument, so it would fail either way.
This commit supplies the extra argument so that the failure should come from the right place.
It also changes the expected error to `ServerActionError` and adds a check
for the message, to verify it is due to missing calibration data.
A future version of the LabThings Client (#89) may raise a different
error if a required argument is missing, so fixing this will ensure
that upstream change doesn't break anything here.
This adds an additional action to BaseCamera to capture and return a PNG Blob. It makes the PNG using Pillow, in a very similar way to `capture_jpeg`.
I have parametrized the test for `capture_jpeg` so it now tests both jpeg and png with the same code.
