Import Handling

[beckyjackson]

Fixes import loading for SPARQL UPDATEs and across chained commands. See #468

[beckyjackson]

I ran the command causing the Travis failure on my system:

$ robot query --input nucleus.owl --update update.ru --output results/nucleus_update.owl
$ robot diff --left nucleus_update.owl --right results/nucleus_update.owl 
Ontologies are identical

When diffing, the ontologies are the same. I re-ran mvn verify and all tests passed.

@jamesaoverton if you get a chance, can you run mvn verify on your system and see if you get a different result?

[jamesaoverton]

This looks good. Just two small suggestions.