Renamed Java SimpleResult to Result

Did the minimum (which was a lot) to get the rest of the code compiling.
Removed last traces of SimpleResult and documented it in the migration guide
Merge pull request #2536 from jroper/remove-java-simple-result

Renamed Java SimpleResult to Result
Fixed Global Errors bug on ScalaForms (issue #2498) and made “Advanced Topics” menu consistent throughout Scala docs (issue #2513)