First fix to issue 341

[KristianKarl]

• Updated the parser g4 file for antlr.
• Updated the events triggered when antlr is parsing.
• Using a new class Node to keep track when the events are triggered, adding nodes representing the various possible stop conditions.
• At the end parse the Node tree to create the final stop condition
• Updated the two toString for the AlternativeCondition abd the CombinedCondition.