Django-esteid

Added Authentication with ID card, Smart ID & Mobile ID.

Also:
* Added pylint.
* Fixed a problem with errors not being handled properly in the SessionViewMixin.
* Changed some EsteidError classes to inherit from InvalidParameters.
* Added deprecation warnings and pragma: no cover to old deprecated modules.

Due to shutdown of the DigidocService:
* Switched to the MobileID REST API;
* Using locally generated signatures for ID card;
* Removed digidoc service support;
* Introduced new signing API;
* Moved ASiC-E container support and certificates into separate libraries.

Implemented DDS-free ID card signing. Dropped support for Python < 3.6 and Django < 1.11. Updated libraries.

- Fix compatibility with `attrs>=19.2.0`

- Add support for ASiC-E (BDOC-TS) containers - see 12

- Removed suds and replaced it with zeep (see 10)
- Added MobileID signature verification (see 15)
- Add helper for parsing RFC2253 Distinguished Names (see 11)
- `Signer.parse_common_name` has been removed (use `esteid.helpers.parse_legacy_common_name`)
- `esteid.digidocservice.models` is moved to `esteid.digidocservice.types` and the types are declared using attr library
- Added all valid SK certs for OCSP and make `OCSPVerifier` slightly more flexible
- Update Django requirements (we now support 1.8 - 2.1)
- Pad OCSP error codes with 4000
- Improve the `IdCardMiddleware` and make it more flexible
- It's now easier to configure it for different servers (Apache/Nginx) and setups (e.g names of HTTP headers used for client certs).
- `DigiDocService`: The following methods now raise `DigiDocNotOk` instead of returning False/None if response status is not OK
- `prepare_signature`
- `finalize_signature`
- `get_signed_doc`

Misc:

- If you relied on `suds.sudsobject.asdict`, use `attr.asdict` as a replacement