Multilayer TIFF Support

[Matesanz]

Description

Enhancement: Add INT16 TIFF support to openSFM

How

Falling back to rasterio library when cv2 fails and normalizing int16 to int8 rgb/grayscale image.

Where in the code:

Changing io.py lines 1016 to 1017: https://github.com/mapillary/OpenSfM/blob/6585f0561e7c9d4907eadc7bc2fb9dbdad8a2945/opensfm/io.py#L1016-L1017

Why:

It would be helpful for processing images with multiple information layers, like the ones used in field analysis. ie.: https://github.com/OpenDroneMap/ODM/issues/1235