Tutorials content fixes

[SolarDrew]

Closes #622 and #623

• StokesCoord introduced in astropy 5.3
• VBI extents -> keep inputs
• Why do array_index_to_world_values? Not clear what I meant by this, if it's important it'll come up again
• Compound physical types present in VISP header example WCS.
• Incorrect dataset ID in mosaic stitching example text
• Keep imports on cryo example imports cell
• Pre-compute image for big cryo plotting example No significant speed up from this, not worth it
• Demonstrate solar angle / distance equivalency
• Use wcs.pixel_shape to show axis names and shapes together, not reverse iterating loop
• Mask out bad files for download rather than just slice Don't think this is actually possible in a sensible way at the moment but it would make a good feature
• More guidance/tips on TickDataset / overlap exercise
• Specify axis_world_coords('lon', 'lat') instead of indexing- (but note it always returns a tuple even if it's length 1, so will have to index anyway)
• Add excercises from latest workshop