Resolution/resampling

[adamjstewart]

Many datasets like Sentinel2 have a different resolution per band. Currently we don't handle this and things crash when you try to concatenate bands with different shape. There are a few options for how to handle this:

1. Automatically resample to the highest resolution
2. Allow user to specify resolution to resample to
3. Store bands with different resolution in different dict keys

Option 3 makes it hard to automatically detect the "image" keys during data augmentation, but offers the greatest flexibility for modeling. Option 1 and 2 aren't mutually exclusive, and are probably the easiest to implement in the short term.

We also need to add transforms for resampling.