Scene Camera view improvements

Few proposed improvements for Scene Camera view (QT3DS-709) as discussed with Soili:

1) Allow also zooming out, so it could be used also to "see the big picture". Meaning levels < 1x, minimum could be e.g. 0.2x. With this, "Perspective View" wouldn't anymore need rendered overview.
2) Adjust zoom level label to always have single digit, so e.g. "2.0x" instead of "2x".
3) Reduce Scene Camera view toolbar height. Make it match closer to timeline toolbar design.
4) Currently view can be panned from everywhere (except on top or slider). Maybe enable panning only when starting pressing on top of rendered view?
5) Consider adding '-' and '+' buttons similar to timeline zooming slider.