* Little improvement to the mouse handling in 3d view

- Rotating around the model does not behave weird anymore.
- Rotation origin is not fixed at the origin of the model anymore.
Instead it moves with with camera.

* Bugfix: Viewport resets transformation after resize

Bug: When the viewport is resized the transformation of the camera is
being reset.
Fix: Restore previous transformation of the camera after resizing.

* Added non-blocking progressbar when loading files

* Small changes to the mouse input