Patch data loader for single-frame ("Static") 2D data

[ngreenwald]

The data loader currently takes the first dimension of the image as the number of stacks, but for 2D data that is the rows axis, not the stack axis. Modified it to only do this for images with more than 2 dimensions.

[MekWarrior]

This PR serves as a temp patch for a larger issue. Under the DeepCell Data Ontology, 2D data are just images - dynamic denotes that you would expect multiple images stored in 1 tif file for a given session and position. For the static branch, it is expected that the each tif would only have one frame in it. But it is all "2D data." The data loader should use either the ontological location or the number of frames to make this distinction and initialize an array of the appropriate size.

N.B. The number of frames is not currently available in metadata but it should be. Once it is available, the array initialization should be handled with a database call rather than calculated on the fly.