Add TreesUser class for improved tree representation and update grammar rules

Q1/Artefacts/RobotLang.g4

@@ -18,6 +18,6 @@ logStat: 'LOG' STRING ';' ;
 repeatStat: 'REPEAT' NUMBER '{' stat+ '}' ;
 
 ID_PREFIX: '// STUDENT ID:' ;
-NUMBER: [0-9]+ ;
-STRING: '"' .*? '"' {self.text = self.text[1:-1]} ;
+NUMBER: [1-9]+ ;
+STRING: '"' .*? '"' ;
 WS: [ \t\r\n]+ -> skip ;