add provider to registry config

this way there is a clear way to disable/remove config

src/views/settings.html

@@ -96,10 +96,17 @@
               <h4 class="modal-title">{{ 'settings.privateDockerRegistryDialog.title' | tr }}</h4>
           </div>
           <div class="modal-body">
+            <p class="has-error text-center" ng-show="registryConfig.error">{{ registryConfig.error }}</p>
+
+            <div class="form-group">
+              <label class="control-label" for="registryConfigProvider">{{ 'settings.registryConfig.provider' | tr }} <sup><a ng-href="https://docs.cloudron.io/settings/#private-docker-registry" class="help" target="_blank"><i class="fa fa-question-circle"></i></a></sup></label>
+              <select class="form-control" id="registryConfigProvider" ng-model="registryConfig.provider" ng-options="a.value as a.name for a in registryConfigProviders"></select>
+            </div>
+
+            <div uib-collapse="registryConfig.provider === 'noop'">
+
               <form name="registryConfigForm" role="form" novalidate ng-submit="registryConfig.submit()" autocomplete="off">
                 <fieldset>
-                  <p class="has-error text-center" ng-show="registryConfig.error">{{ registryConfig.error }}</p>
-
                   <div class="form-group">
                     <label class="control-label" for="registryConfigServerAddress">{{ 'settings.privateDockerRegistry.server' | tr }}</label>
                     <input type="text" class="form-control" ng-model="registryConfig.serverAddress" id="registryConfigServerAddress" name="serveraddress" ng-disabled="registryConfig.busy" placeholder="docker.io" ng-required>
@@ -121,6 +128,7 @@
                   </div>
                 </fieldset>
               </form>
+            </div>
           </div>
           <div class="modal-footer">
               <button type="button" class="btn btn-default" data-dismiss="modal">{{ 'main.dialog.cancel' | tr }}</button>