Initialize Neuroglancer at t=0 to avoid odd behavior

Viewer links for the cell segmentation states behave differently than the stitched volume links. See [here](https://github.com/google/neuroglancer/issues/772).

This boils down to the initial position of the viewer being at t=0.5. When a user presses z to snap a rotation to the nearest data-aligned axes, the time axis snaps to t=1, which is out of bounds for the zarr volume and causes the image to disappear.

The nglink functions used to create the stitched volume link must take care of this, since the behavior is not observed there. I think the position can easily be added here:
https://github.com/AllenNeuralDynamics/aind-SmartSPIM-segmentation/blob/4d6b2495bbcf442c547dd73e0d227e88ff93a72e/code/aind_smartspim_segmentation/segmentation.py#L318