Recognise PENDING status in sequence imports.

If a final sequence file or directory name matches a pattern
which is recognised to indicate a ‘pending acceptance’ status,
the final data (if any exists) for that sequence will be deleted
and a comment added to the effect that the sequence has been
marked as ‘pending’.

To accept the sequence, rename its final file or directory name
accordingly.

Note: it is the *final* data that is searched for a matching
pattern, not the raw.

Closes #91.

bin/system_imports.py

@@ -40,6 +40,10 @@ if __name__ == '__main__':
 				continue
 
 			try:
+				for table in exportables:
+					path = os.path.join(pathPrefix, table)
+					if os.path.exists(path):
+						cursor.execute(f"DELETE FROM {table};")
 				for table in exportables:
 					path = os.path.join(pathPrefix, table)
 					print(" ← ", path, " → ", table)