Clean repo & release-script (#1717)

* Change build-script to leverage composer archive

* No longer include data/ cache/ and log/ directories. They don't belong in the install-dir

* Remove unnecessary .gitkeep files

* Merge config&config-templates and metadata&metadata-templates; templates renamed to .dist

* Reduce git clone overhead

* Throw an exception if datadir not set

Co-authored-by: Thijs Kinkhorst <thijs@kinkhorst.com>