Javaparser

Java parser for dotty.

As we discussed, three tests are still failing:
* t2409:
  Requires import of companion object before first constructor.
* t1751 and t294:
  Tree transformer does not transform repeated method arguments within an annotation instantiation.

Review by @odersky @DarkDimius


Does Enum flag in scalac have the same meaning? 
if yes it would be good to add it to flag mapping that is used while reading scalac flags(see `PickleBuffer` class)