Add string value for measures.

[tjhrulz]

While it may not sound needed it would be nice especially for debugging purposes if the measures had a string value, I could also see some uses where some may want an OnChange event on the measure or may just want to be able to access the value from somewhere else and do string manipulation. Bonus points if it also knows if RelativeToSkin is enabled and is a relative value in such a case.

[tjhrulz]

Also would be useful for getting around the mouse down events don't fire if the measure was enabled in a different mouse down, since iirc that would not be fixed unless you could find a way to handle the measure enable and disable events yourself.