* Add a UserKeyToken to the User table for Kobo authorization.

* Add proper authorization checks on the new Kobo endpoints.

Important Note: As a side-effect, all CalibreWeb API calls can be
authorized using this token (i.e without a username&password).

cps/templates/user_edit.html

@@ -28,6 +28,10 @@
       <input type="email" class="form-control" name="kindle_mail" id="kindle_mail" value="{{ content.kindle_mail if content.kindle_mail != None }}">
     </div>
     <div class="form-group">
+    <div class="form-group">
+        <label for="kobo_user_key">{{_('KoboStore UserKey')}}</label>
+        <input type="password" class="form-control" name="kobo_user_key" id="kobo_user_key" value="" autocomplete="off">
+    </div>
     <label for="locale">{{_('Language')}}</label>
         <select name="locale" id="locale" class="form-control">
             {%  for translation in translations %}