Implement creating new App from other App Creation dialog.

Any field type unspecified in dynamic UI code is considered to be
fully qualified name (FQN) of some Application. Currently only apps of
that exact FQN will be present in drop-down list, in future all
descendants will also be supported.

New form field/widget (as well as js-code) is taken almost ready from
horizon.forms.fields.DynamicChoiceFields, with a bit of copy-paste
from horizon in django Wizard done() method (it is not possible to
directly inherit the required functionality from
horizon.forms.views.ModalFormView, because it is incompatible with
django WizardView.

Change-Id: I942884a9a98857c13002095c8d8bb96331d2e555
Implements: blueprint new-web-ui-prototype