Improved handling of the input for TextPresenter

Also, I fixed the problem where pressing the A key doesn't insert any text.
Please, note that I omitted the "this" keyword. This is much discussed, but I have researched to form an opinion on this coding style. Anyone that needs justification, please, contact me.

Thanks :)
Hmm, unsure about this - in one way it reads better but key.IsPressed(ModifierKeys.Ctrl) isn't any shorter than ((key & ModifierKeys.Ctrl) != 0) and the second is idiomatic...