Add contao44 package version 4.4.0.

Contao 4.4 is fourth minor release of Contao 4 and it is LTS (Long Term
Support) release until June 2021.

Additionally, these new features from 4.3.

* Improved backend theme
* Improved element preview
* Detect version conflicts
* Improved handling of image meta data
* Details view contains path addition to their UUIDs
* Honeypot anti-spam
* Allowed member groups
* Import options for some form fields
* DCA picker
* Filter pages and articles
* Search files
* Contao Manager support

(taca)