This allows users to create their own mapping file to extend our current
mappings. This makes sure that custom mappings are not lost on OC
upgrades.

This allows users to add new mimetypemappings (extention -> mimetype)
themself. And not have to wait until a new release for updated
mimetypes.

Fixes: #15384

[config sample] improve RST markup and wording

Remove 3rd party text for disabled apps on update

Keep update page when there are warnings

autotest.sh with docker support for postgres

Add "occ config:*" to manage config values

Whenever there were warnings during an update, the page will not be
redirected any more.

PHP mimetype stuff should also use config/mimetypealiases.json

Update version to 8.2 in README and bower

[config sample] Update info about appstore

Javascript to fetch mimetype icons

Fix regression of button at public download page