Make Tern.java to be able to treat a custom project nature as Tern nature.

This will allow Tern.java to be seamlessly integrated to other products.

Signed-off-by: vrubezhny <vrubezhny@exadel.com>
Merge pull request #38 from vrubezhny/makeTernAdaptableToOtherNatures

Make Tern.java to be able to treat a custom project nature as Tern nature