bluViewport: Added zoom!

Also
* When the viewport is an odd-numbered width, the zoomed image will not
get a wonky pixel row/column
* Less unnecessary repaints, reducing potential flicker and increasing
speed
* MouseMove event fired when zoom is changed
* Fixed frmPlay not getting focus when clicking on the main tabs
bluViewport: Set focus when clicking scrollbars

Allows you to click the scrollbar and use the keyboard to scroll.