"New X10 Project" wizard should be X10-specific

The current "New X10 Project" wizard extends the "New Java Project" wizard.

As a result, it depends on the JDT's project configuration meta-data, which isn't sensible when the project targets the X10/C++ back-end. Also, it shows Java-specific information that doesn't make sense in an X10 context.

This relies on having X10-specific project configuration meta-data, and thus is strongly coupled with other parts of the X10DT that consult/modify project configuration meta-data (like the Project Properties dialog or the X10 launch configuration editor).