More retries on rate-limiting

[patr1ckm]

This increases default retrying for call_api. Changes:

• When rate limiting, all verbs can be safely retried. Fixes #201 .
• Increase the default retries to 10, with maximum wait time for 1 hour. Fixes #210 .
• Fix assumption in error handling that an errorDescription field is provided in the response (it isn't for at least 429). Fixes #213 .

The smoke tests successfully ran locally.

Do you mind one last civis-r code review @keithing ?