Limit processing by image resolution

[mzur]

There are cases where non-tiled images are still too large for inference on the GPU. This highly depends on the available GPU memory. Implement a config value for a megapixel threshold that is used to limit processing of MAIA jobs to images of a certain size. Either MAIA skips these images (with a warning message when the job is created) or MAIA jobs are disallowed for volumes containing these large image altogether.

When implemented, this can replace the existing check for tiled images, as these images would have too many megapixels as well.

[mzur]

Novelty detection can now handle very large images, too (see #117). Object detection still not.