Prevent unexpected access to other types using reflection for security

[davideicardi]

We should disable code that use reflection in a malicious way. For example if I reference type X inside the interpreter I should not be allowed to write an expression like:

typeof(X).Assembly

Because potentially in this way you can access and invoke any type defined in that assembly.
The same can be for instances:

xInstance.GetType().Assembly

Think about other similar security problems...

[davideicardi]

Prevent unexpected access to types using reflection for security (#27) . From now expressions that call reflection throw a ReflectionNotAllowedException.
Added Interpreter.EnableReflection method to enable reflection features inside expression.