Implemented Consoloid.Interpreter.ExpressionTree (refs #6)

It has one additional public method: removeExpressionsOfTopic.
Consoloid.Ui.Console: It now has unloadTopic method (Refs #6)

For this to work it also adds topics to sentence instances.
tutorial.services: Added a sentence that starts tutorial (refs #6)
Consoloid.Tutorial.UnloadDialog: Added dialog that unloads the tutorial topic (refs #6)