Fix warning in filecache gc

Add default value for remote_id

Fix file move/copy when storage space is not enough

clarify link on apps management to the dev documentation

Move UTF-8 check to setup

Fixes WebDAV copy

Append search results to custom container

Add async command system to handle asynchronous operations

Remove dependency from arbitrary data object structure for easier usage

Remove uneeded assignment

Fixes SQLite migration with non-null column.

Failing mysql master tests

Clean up AppFramework database layer

using Doctrine\DBAL\Connection::executeUpdate()

Show 404 page when accessing empty share URL

Return null when requesting tags for null user

Remove unused and deprecated Code

Message clean-up

Testplan:
- [ ] Without: Accessing `public.php?service=files&t=` throws an exception
- [ ] With: No exception thrown and 404 page displayed.

Fixes https://github.com/owncloud/core/issues/14231

The TagManager->load() now returns null if the user is not authenticated
instead of failing with an error.

- added existence check for source argument
- removed extra logic for folders, as $view->copy() already supports
  that internally

Now checking whether the written bytes match the number of read bytes.