Add support for writing sidecar files for raw images

Updates #267

Notes:

Currently only applies to the CLI; see #232 for GUI support
By default, if a raw image path is specified and it has a sidecar, that sidecar will be used
If sidecar setting is enabled in settings.yml, a new sidecar file will be created for a raw image if it does not exist
Behavior applies to any file that isn't a supported image type (i.e., there's no hardcoded list of raw file extensions)
Behavior applies to file paths or glob patterns, but not for directories

pyinat / naturtag