Avoid forcing data type for image arrays

[wronk]

In some places we force the dtype to be uint8 (i.e., integer on interval [0-255]). See package.py for an example.

In some situations, we might want to package tifs or raw satellite imagery where the data either isn't made up of integers or doesn't fall on this [0, 255] range. For example, it might be pre-scaled from [0-1] or extend beyond the standard range of RGB vals.