Make scrooge generator import jars instead of having to extract them

https://github.com/twitter/scrooge/blob/develop/scrooge-generator/src/main/scala/com/twitter/scrooge/frontend/Importer.scala#L56 makes it appear that we can import jars, but some quick tests didn't work. Still, would further simplify our code

Start with scrooge-generator/src/main/scala/com/twitter/scrooge/frontend/Importer.scala at line 56 and reproduce the quick tests that failed to import jars. Trace the current import behavior and confirm the work is done when jars can be imported without extraction and the relevant tests pass.

Written by the indexing model from the issue text.