Implement the ModelJoin parser using ANTLR

build.sbt

project/build.properties

src/main/antlr4/ModelJoin.g4

..._join/representation/grammar/KeepAggregateExpression.java

...join/representation/grammar/KeepAttributesExpression.java

...join/representation/grammar/KeepCalculatedExpression.java

...ync/model_join/representation/grammar/KeepExpression.java

..._join/representation/grammar/KeepReferenceExpression.java

...el_join/representation/grammar/KeepSubTypeExpression.java

..._join/representation/grammar/KeepSuperTypeExpression.java

...ync/model_join/representation/parser/ModelJoinParser.java

...join/representation/parser/ModelJoinParsingException.java

...presentation/parser/antlr/AntlrBackedModelJoinParser.java

...oin/representation/parser/antlr/JoinStatementVisitor.java

...oin/representation/parser/antlr/KeepStatementVisitor.java

...el_join/representation/parser/antlr/ModelJoinVisitor.java

.../representation/parser/legacy/DefaultModelJoinParser.java

...c/model_join/representation/parser/legacy/JoinParser.java

...c/model_join/representation/parser/legacy/KeepParser.java

...ect/model_sync/model_join/representation/util/Assert.java