[UI] Implement App Catalog pagination similar to Glance images pagination

API entry point for AppCatalog - search() function should return dictionary with 'packages' and 'next_marker' values - similar to Glance index() function (https://github.com/openstack/glance/blob/master/glance/api/v2/images.py#L94). Then a generator in python-muranoclient filter() function could be based on that data (similar to https://github.com/openstack/python-glanceclient/blob/master/glanceclient/v2/images.py#L38). Finally, it should allow paginating complex query results at dashbord's App Catalog page.