Remove DataFormProvider from extension.providers

XEP-141 Data Forms are never used as stand alone packet extension, there
is no need to register the provider with the ProviderManager.

This makes the parse method of DataFormProvider static.
Change DataFormProvider to new style provider design

By using e.g. string-switch/case.
Add XData(Layout)Manager

to register the features with ServiceDiscoveryManager for XEP-4 and
XEP-141.