[Master] sync upstream

Get rid of LGTM self approvals

* add missing spaces

Add app:check-code for already compatible apps

Theming app

Allow regular users to specify global credentials password

add events to check passwords with the password policy app

* admin_audit, comments, federation
* removed not needed call to OC_Util::checkAdminUser() (is already
  done by the request handler before)

Add "Login credentials" and "User Provided"

Quickfix: do not lazy load auth mechanisms for ext storages

Prerender file list pages to include search results

show which login name to use for the new app password

While the UI is existent the feature simply doesn't work because admin privileges are required for the controller. This adds proper permission checks and also unit tests.

To test this:
1. Enable external storage
2. Login as non-admin user
3. Go to personal page and try to change global credentials

Keep encryption enabled if decrypting for single user

Add explicit delete permission to link shares

Make code integrity check work when OC is not installed yet

Some auth mechanisms like SessionCredentials need to register hooks
early, so they cannot be lazy loaded.

Remove tooltip when disconnecting token

The app is now enabled by default

Otherwise dropping something somewhere can by mistake upload the file and make it available

AppManager has a dependency on Nc being installed

Also adds support for having custom login backgrounds