IVS-492 - API Rate Limiting

[rw-bsi]

Current configuration:

• allowed to submit 10 Validation Requests per hour via the API
• allowed to list/retrieve info via the API at a rate of 1000/hour (or 100/hour if anonymous, which we don't allow)

'DEFAULT_THROTTLE_RATES': {
        'anon': '100/hour',
        'user': '1000/hour',
        'submit_validation_request': '10/hour'
    }

[Ghesselink]

Can you wait with merging this into development until after the 0.7.7.1 release (it's a bit delayed, sorry)