Yoti

Added
- `document_images` attribute, accessed through `profile.document_images`, using new `Image` type
- `int` content type (accessed through `profile.get_attribute(attribute_name)`)

Changed
- SDK Version header value
- Regenerated protobuf files, removed version folder

Removed
- `tox` package (in favour of testing with Travis)

Security
- Updated packages

Added
- `parent_remember_me_id` to `activity_details`
- Python SDK version to HTTP headers

Added
- To ActivityDetails:
- receipt_id
- timestamp
- `email_address` getter to new profile class

Security
- Updated `cryptography` package

Added
- new `profile` object, which includes:
- anchors, sources & verifiers on each attribute
- further retrieval of properties from these anchors: `value`, `sub_type`, `timestamp` and `origin_server_certs`
- helper methods for each attribute

Changed
- `Yoti`, `Django` to be stricter version requirements
- Updated `cryptography` required version to >= 2.2.1

Deprecated
- `user_profile` object on `activity_details` (use `profile` instead)

Added
- `structured_postal_address` attribute

Changed
- If `postal_address` is null, it is taken from StructuredPostalAddress.FormattedAddress (if present)