Fix broken inferlink example

[donaq]

trying to run python inferlink_example.py gives the following error:

Traceback (most recent call last):
  File "inferlink_example.py", line 35, in <module>
    docs = etk.process_ems(doc)
  File "/home/donaq/progs/etk/etk/etk.py", line 168, in process_ems
    if self.kg_schema.legacy:
AttributeError: 'NoneType' object has no attribute 'legacy'

This is because the call to ETK() in the example code does not provide a value for the kg_schema argument, which defaults to None. Since that is a possible value for kg_schema, process_ems should check for it.

[saggu]

@donaq please change the target branch to development

[donaq]

@saggu Ok sure. It's done.