Keep focal mechanism info during merge

[kirstybayliss]

Changes to catalogue merging tools to keep the focal mechanism information from catalogues where we have it. Specifically:

• changes to gcmt_catalogue so that information is retained in preprocessing steps
• changes to generic catalogue parser so that retained information is correctly read and passed on
• changes to isf_catalogue so that focal mechanism data is added to earthquake location information and passed to origin output
• changes to utils so that the final step of creating a csv checks if we have focal mechanism info and passes it on if we do
• updated line number in isf_catalogue_test