Encoding category into ResourceKey

[anibalsolon]

I believe it would be better to add this info to the ResourceKey, instead of trying to infer it from the suffix (as in https://github.com/radiome-lab/radiome/blob/develop/radiome/utils/bids.py#L6)

e.g.

ResourceKey('anat/sub-001_ses-002_space-orig_T1w')