Improve fileshare handling, error handling.
Improve fileshare handling, error handling.

- 'upload' request class removed, not currently supported.
- `raise_for_status` function to add error response if given.
- Response decoded unless request class is download.
- Handle rate limit exceeded for modeldef requests.
- `_get_predicate_fields` method removed, holdover from
  first try at implementing keyword checking.

python-astrodynamics/spacetrack