Avoid postion - index conversion in view

[ivmartel]

These conversion could lead to rounding errors, resulting in, for example, the rejection of a setCurrentPosition which would then not draw the image at that position. This is what is happening in dwv-jqmobile/issues/79 (no scroll).

The view must work internally with index and only take position from external, such as the binding between layers.

[ivmartel]

...but using an index means you are dependent on the geometry, if it changes, the index is not correct any more. This can happen during load, a first geometry is created for the first slice and it can be updated with other coming slices. The slice is displayed correctly but a scroll will lead to a completely different position.

This change must be reverted and another solution found for ivmartel/dwv-jqmobile#79.