Implement restricted pages and documents

[fgrsnau]

Instead of only publishing a few minutes, we want to make all minutes available to our members. This merge request should prepare Sipa for this change by

• introducing a restricted documents area where the authentication of the user is checked
• introducing a new meta field that flags the FlatPage as restricted

Up to now I did the following:

• Run the tests and see them pass
• Rebase your branch on top of develop
• Include tests for features you introduced / bugs you fixed

[lukasjuhrich]

Since you asked in private on how to compose unittests, it goes along the lines of this:

from ..base import SampleFrontendTestBase


class RestrictedDocumentsUnauthorizedTestCase(SampleFrontendTestBase):
    def setUp(self):
        super().setUp()
        # here you can set up things and add attributes to taste


    def create_app(self, **kw):
        # here you can create a temporary directory with e.g. a global
        # file and one in a folder `restricted/`.
        conf = kw.pop('additional_config')
        conf = {
            **conf,
            # here you can update the apps config, i.e. add the document base
            'CONFIG_VAR': 'testing'
        }
        kw['additional_config'] = conf
        super().create_app(**kw, additional_config=conf)

    def login(self, username, password):
        """login `username` with `password`.

        This method doesn't actually belong in this test case, but I
        noticed that no test base provides either a login mechanism.

        The `sample` backend has a user with {'uid': 'test',
        'password': 'test'}.
        """
        pass

    def test_unauthorized_404(self):
        resp = self.client.get('/documents/restricted/foo')
        self.assert403(resp)  # or assertRedirects, depending on what is done

For an example of a login mechanism, see test_basic.py (which is actually unused, kek).
See also the reference of flask_testing to have an overview of the custom assert methods.

[lukasjuhrich]

Since I don't have permission to push to your branch, I rebased and developed further on origin/restricted-documents.