Add query tests; Make tuplestream operator handler function configurable in querycompiler; Register external functions used for version_management;

Add TupleStream as new physical root operator; Move methods of value transformation to seperate class

Add version tag recognition for update statements; Solve bug caused by not checking if tuple is visible in Tablescan operator

Add version recognition for insert statements; Add version recognition for select statements; Modify TableScan operator to store the pointer to the alias; Modify version_management to take the version of the current table; free memory after using alias

Change return type of semantical analysis to operator instead of result; Add update operator which can be used as a node in the query tree; Fix bug with pushing up tids