Add an option to report Java errors

[renaudpawlak]

Currently, JSweet prints out Java errors bud does not go through the actual error reporting API (see the bad looking TranspilationHandler.reportSilentError() method). This is bad for reporting compilation errors in a consistent way.

We need a solution for reporting or ignoring Java errors depending on if the reporting of Java errors is needed or not (for instance, in the Eclipse plugin, it is not needed because Eclipse will report the errors).

Possible solutions are:

• add an option to the transpiler, so that it can ignore Java errors
• add a category to errors so that the handler can ignore some of them

The second solution is probably better... clearly more generic and flexible.

[renaudpawlak]

All Java errors are now reported as JSweetProblems.INTERNAL_JAVA_ERROR, so that the transpilation handler can choose how to report them.