Clean up imports

[sebastianduesing]

This PR includes the following changes to clean up the OntoFox import files, in order to streamline my upcoming attempt to transition OBI from OntoFox to ROBOT imports:

• Remove redundant subClassOf assertions, i.e., those that are true within the source ontology and thus don't need to be stated in the import file.
• Remove instances of multiple import statements for the same IRI.
• Sort all import statements and subclass assertions numerically by IRI. For subclass assertions, this goes by the IRI of the subject, e.g., the lines that assert CL_0000001 subClassOf CL_0000010 sort above the lines that assert CL_0000003 subClassOf CL_0000000
• Add a comment labeling every IRI with its term label for every import statement & subclass assertion line that doesn't already have its term label in a comment.

This is purely a tidying-up of the import text files themselves; these changes are designed have no effect on what OBI is actually importing. Running make imports etc. on the cleaned-up files results in zero changes to the output OWL files. The only OWL files diffs that appear in this PR are the result of an import refresh I did to make it easier to test the previous statement, and those changes will no longer show up in the diff with master once #1849 is merged.