Add a configuration switch for enabled preview mimetypes

Backport of https://github.com/owncloud/core/pull/11211 to stable7
Merge branch 'stable7' into backport-11211

Conflicts:
	config/config.sample.php
Updating 3rdparty - contains updated tar archive and getid3
Show a proper error message when trying to scan the filesystem for a non existing user
Merge pull request #11245 from owncloud/backport-11211

Add a configuration switch for enabled preview mimetypes
Clarify possible preview providers for type Office

a

Conflicts:
	lib/private/preview.php
Don't keep the full info of all children in memory
Expose creatable permissions trough fileinfo
Fix dav permissions for folders without create permissions
for whitelabeled edition, show branding name (e.g. 'ownCloud') instead of appname in header bar
Added spinners in share dropdown

Added spinners for the following actions:
- adding user
- removing user
- changing password
- toggling allowing upload
- setting a password
Add ID to markup to have the checkboxes in the right position
Prevent monkey clicking on labels

Clicking on labels while the spinner is there will not trigger the
hidden checkbox any more.
Clear up confusion of log_rotate_size config value

Remove the second comment which could be confused with suggesting an invalid value: `// 100 MiB`.

To keep the easily readable example value, it has been moved into the comment header for the config item.
dn needs to be fetched to be able to detect memberOf support
Close the session for preview generation

Without closing the session every preview image generation is locking the session which makes the webinterface unresponsive.
don't clean up the test environment if a data provider was finished
Merge branch 'stable7' of https://github.com/owncloud/core into stable7