Create adhocracy modules

This PR creates 3 new modules:

- `AdhocracyEmbedder`, which realizes the connection with the `AdhocracySDK` frontend embedding API (it doesn't talk to the Adhocracy backend)
- `Auth`, which provides login functionality (which is realized by embedding Adhocracy)
- `Deliberation`, which provides discussion functionality (which is also realized by embedding Adhocracy).

The modules don't work if Adhocracy isn't available, therefore the config entry `ENABLE_ADHOCRACY` is set to `false` by default.

The first commit (cc37e8d) exposes the PolicyCompass config as a global variable, which is a bit ugly, but I'm not aware how to do dynamic module loading in `app.js` using dependency injection.

The Auth services is basically done - if Adhocracy is available and enabled in the PC config, the Auth service sets the proper Auth headers for all calls which use the angular `$http` service, if one logs inside the embedded Adhocracy.

The deliberation directive `showDiscussion` will change its interface in the upcoming weeks. At the moment, it requires an existing Adhocracy commentable as an argument:

    <show-discussion data-path="http://localhost:6541/adhocracy/dede/VERSION_0000001"></show-discussion>

This will later be changed to something which might more look like the following:

    <create-or-show-discussion data-context-url="http://policycompass.eu/api/v1/metrics/7"></show-discussion>

If someone has the time to look at it, feel free to comment or merge, otherwise it's okay for us to keep this in a branch, until the full functionality, including easy Adhocracy deployment can be provided by LIQD. This PR is at the moment mainly meant to keep the others informed of the state of development of PolicyCompass-Adhocracy integration.