protect UIMA Class loader in multi-threaded get resource contexts

I have seen one case where multiple threads were being used where a UIMA Class Loader was being used to load a resource (Type system Descriptor -> type System was resolving an "import by name"), where the getResource returned (only once) a spurious "null" result.

This is likely due to some multithreading issue in get Resource.  Add a sync using the same multi-threaded parallel approach used for class loaded, to getResource, to protect against this case.