Improve missing imports resolution fixes #676

[onor13]

1. Possibility to resolve missing imports from XML Catalog and not only an
   ontology file.
2. Possibility to change the active catalog.
3. Fix: the classes hierarchy is not reloaded when adding “Direct Imports”
   in “Imported Ontologies” window

[csnyulas]

Thank you for your contributions @onor13 We will test it early next week and if everything seems okay, we will merge it with our branch.

[onor13]

By the way, it's me, Vladimir. I'm the one who had trouble uploading plugins to the protege wiki (because of the constant log outs), that you helped me with recently. I also would appreciate if somebody could look at my fix in Xml Catalog project: protegeproject/xmlcatalog#10, unless you are planning to use Java 9 JDK, as soon as it comes out, then the whole xml catalog project became obsolete, because Java 9 has an XML catalog library.

[csnyulas]

Hi Vladimir.
Nice to see that you are active on our github as well :)
We'll take a look at the other pull request as well.

[onor13]

Hi, it's been almost a month, did you had the time to test? Or you did the tests and you don't approve of my changes.

[csnyulas]

Sorry, Vladimir. I dropped the ball on this. It's been very busy here lately, and I forgot about this. I will try to take a look at this this week. I am really sorry! Thanks for the reminder, though.