Enable autoconvert in GssResourceGenerator.

This is still guarded by a flag and needs to be turned on by each app.

fixes #108
you should pass "[auto-converted css files]" as fileName:
```Java
sourceCodes.add(new SourceCode( "[auto-converted css files]", gss));
```
or at least modify the method report of the inner class LoggerErrorManager.

Otherwise, the log will display error message like this:
"Error in null [line: X, column: Y]: ..."