fix small bug in new justify attributes

When the `justify`, `middleJustify`, and `bottomJustify` attributes were added, all three changed watchers were using `this.justify` instead of their respective attributes, so only one justify style would be applied to all three divs.  This has been corrected.  Also, some new verbiage was added to the comments at the top of the file to indicate a difference between `tall` and `medium-tall` class behavior.