Added Avocet journals-module.

### Importing journals
Importing journals is only enabled for global- and tenant admins. To import a set of journals, a `POST` request needs to be sent to `/api/journals/import`. 
```
    'data': {
        'journals': file.csv
    }
```

The `.CSV`-file must be constructed in a way where the first 'column' contains the name of the journal (e.g. "Academic Research"). The second and third column contain the "print ISSN" and the "electronic ISSN" (e.g 1553-1963).

### Searching for journals
Since we want to use the journals for an autosuggest feature in the front-end, we registered a search endpoint. Searching for journals can be done using the `/api/search/journals` endpoint. The endpoint accepts the 'q', 'limit', 'start' and 'sort' parameters (e.g. /api/search/journals?q=academic&limit=10).