Necessary change to solve https://github.com/ceylon/ceylon-ide-eclipse/issues/761

Change the name of the default package to a list with one empty string (instead of a void list of string). This is needed to be consistent with
the way the Java backend manages it. Consistency between front-end and
backend here is needed to allow the backend to reuse the model existing inside the IDE.

FYI : ant test on ceylon-spec were successful, as well as the compilation of the SDK within the IDE with this change.