1. Renamed the Image menu items "Mirror Vertical" and "Mirror Horizontal" to "Flip Sideways" and "Flip Upside Down", respectively. This also involved changing the code to match the new names, for consistency.
2. Fixed a bug where zooming in and out would result in the image moving off center. This was due to the bitmap width and height not being recalculated after applying the zoom factor and therefore throwing off the calculations to find the rect for the center.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@17182 a95241bf-73f2-0310-859d-f6bbb57e9c96
