They only serve purpose in Github Actions

* Move www > public

* Remove local assets

* Import remotely generated assets

* Update files to reflect www > public move

* Update upgrade notes

* Make assets-filter aware of new assets-location

* Update test-framework

* Exclude generated assets from code sniffer

* 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>

Commit 1edc1264 replaced Travis CI with GitHub Actions. Remove the
remaining references to Travis CI.