Changed StatementTypeChecker to check types over multiple statements
Changed SupportedTypes class to support contains / get based on value
Changed StatementChecker to support checking over multiple statements
Refactored ComputedQuestion unit tests to check over multiple statements
Put override equals / hashCode into LiteralExpr super class
SupportedTypes class now uses equals method from super class
Removed custom contains / get method because of new overriden equals method
Renamed SupportedTypes to TypeEnvironment