Fix default values for acr

Allow testers to run specific tests

Add requested authn context for backend requests

Refactor attribute profile initialization

Use acr_mapping from the backend config to generate a
RequestedAuthnContext node in an AuthnRequest.

acr_mapping configuration is extended so that each entry is a dictionary
with two possible keys:
- class_ref: defines the content of the AuthnContextClassRef node
- comparison: defines the Comparison attribute

Until now the command 'tox' would run all of the tests.
With this change one can specify a test to be run by running:

    tox -- path/to/test.py

Select preferred binding on the configuration

pysaml2 supports the configuration option 'preferred_binding' which is
a map of services to array of preferred bindings for that service. Use
the configuration instead of the currently hardcoded choices.

An example configuration would be the following:

  module: satosa.backends.saml2.SAMLBackend
  name: Saml2
  config:
    sp_config:
      preferred_binding:
        single_sign_on_service:
        - urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Redirect
        - urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST

This defines the preferred bindings for the SSO service, and is
equivalent the code that was hardcoded before. Changing the order of the
bindings would use HTTP-POST instead of the HTTP-Redirect.

Fix codeblocks in Custom attribute release section

Update documentation link for eIDAS Message Format from v1.0 to v1.1-2

Merge branch 'feature-linkedin' of https://github.com/saxtouri/SATOSA into saxtouri-feature-linkedin

Support ORCID OAuth2.0 backend

Expose metadata endpoint via configuration option

Add attribute processor microservice

Store outstanding queries to disallow unsolicited responses

Correctly handle error responses

In case of an error, reflect the state to the client in the error
response (if the client sent a state parameter in the original
request)

Check for configuration option 'entityid_endpoint'.
When set to true the metadata will be served at the entityid URI.

Add custom logging microservice

fix for bad config check on sensitive keys

Upgrade pyop to v2.0.5 in order to fix #92