[tests] add relevant tests for m2l (ongoing)

[lachlangrose]

This is an ongoing issue to keep track of tests that need to be added to map2loop

• intrusions: conformable stratigraphy with a dyke running through. Expected result is the contacts of stratigraphy near the dyke are ignored
• colour maps: test where clut file doesn't exist, where it is missing units, where it has invalid colour codes and where it is valid
• missing files: missing files for all inputs of m2l, either raise FileNotFound exception or continue if the file is not critical.
• faults: make sure that the basal contacts are cropped near the faults, displacement calculation is relevant