Add comment and spacing tokens to the Java ANTRL4 grammar

[green-coder]

Those tokens are skipped in the current grammar file:

//
// Whitespace and comments
//

WS  :  [ \t\r\n\u000C]+ -> skip
    ;

COMMENT
    :   '/*' .*? '*/' -> skip
    ;

LINE_COMMENT
    :   '//' ~[\r\n]* -> skip
    ;