gui: Handle slices in advanced config, show devices in advanced config (fixes #2267)

The ng-list directive makes angular handle lists by doing comma
separation in the roundtrip. We could simplify our normal config dialog
this way as well...

Also adds devices that were inexplicably not available in the advanced
config.

This reveals some other uglyness, as the "devices" config of a folder
now shows as "[object Object], [object Object]" - previously it was
invisible. I think that's fine for now.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4071

gui/default/syncthing/core/syncthingController.js

@@ -1743,6 +1743,9 @@ angular.module('syncthing.core')
             if (typeof value === 'boolean') {
                 return 'checkbox';
             }
+            if (value instanceof Array) {
+                return 'list';
+            }
             if (typeof value === 'object') {
                 return 'skip';
             }