Panoptescli

- Update panoptes-client requirement to >=1.6
- Bump humanize to <4.8
- Fix: Remove deprecated U mode in file open
- Update README with iNat and python 2 deprecation info.

- New: support `%` in manifest column headings for indexed subject sets. Manifest headers with the `%` prefix will automatically be added to the subject set configuration `'indexFields'` list.
- New: iNaturalist observation import functionality (see --help for details)
- Update reqs for humanize, click, pyyaml, & pathvalidate

- Update panoptes-client requirement to >=1.3

- Bump pyyaml to <5.4
- Bump humanize to <1.1

- Fix: Bump pyyaml requirement to >=5.1 to fix AttributeError

- New: Use multithreaded subject uploads
- New: Add option to resume subject uploads on failure
- New: Add ID file option to subject set add/remove
- New: Add `--file-column` option to subject uploads
- New: Add `info` commands for all objects
- New: Add `delete` commands for all objects
- New: Allow multiple remote MIME types
- New: Add `user token` command
- Fix: Do not connect to API during `configure`
- Fix: Use `yaml.full_load` instead of `yaml.load`
- Fix: Use `os.path.isfile` instead of `exists`
- Add help text to `workflow download-classifications`
- Abort uploads if manifest doesn't contain any rows
- Don't show password in configure command
- Validate endpoint config
- Validate file sizes before uploading
- Update pyyaml requirement to >=3.12,<5.2
- Update click requirement to >=6.7,<7.1