Fix eclipse_gen idea_gen for targets with both Java and Scala

eclipse_gen.py was completely broken:
* Use self.context instead of argument (fixes 1d68bf9d0c)
* Add missing templates
* Fix paths to jars in generated .classpath
* Add test_eclipse_integration.py based on test_idea_integration.py

Both Eclipse and IntelliJ generators were broken for targets that depend on a
library with both Scala and Java source code. They failed to add the Java
dependencies.

ide_gen.py: recurse into Java source dependencies for ScalaLibraries
scaladepsonboth: Example target that depends on a mixed Scala/Java project

Testing Done:
PANTS_DEV=1 ./pants goal test tests/python/pants_test/tasks:integration

I also verified that both IntelliJ and Eclipse can build the generated project for src/scala/com/pants/testproject/scaladepsonboth. The current master doesn't work on either, due to missing a Java source dependency.

Reviewed at https://rbcommons.com/s/twitter/r/857/