SortBy updated to handle desc, minor fixes

src/qir/ast/data/QIRLcons.java

src/qir/ast/data/QIRTcons.java

src/qir/ast/operator/QIRGroupBy.java

src/qir/ast/operator/QIRSortBy.java

src/qir/driver/QIRDriver.java

src/qir/visitor/IQIRVisitor.java

src/qir/visitor/QIRCompileVisitor.java

src/qir/visitor/QIREvaluationVisitor.java

src/qir/visitor/QIRFreeVarsVisitor.java

src/qir/visitor/QIRGreedyReduceVisitor.java

src/qir/visitor/QIRSQLStringVisitor.java