Update manager.php

add caching to getUserGroupIds
Update manager.php

added description and blank lines in getUserGroupIds
Update manager.php

defined $uid in getUserGroupIds
Update manager.php
Update manager.php
Update manager.php
clean up function getUserGroupIds

clean up of function getUserGroupIds and improved caching mechanism of cachedUserGroupIds
modified caching mechanism in getUserGroupIds

removed cachedUserGroupIds, instead changed indexing in getUserGroups to groupId
adapted tests for a groupId indexed group array
fix in displayNamesInGroup: when specified limit N, we did complex search only in the first N users
fix orientation in image-backend, not in preview system itself
Fixed file list sorting

Now using a natural sort algorithm that is more consistent between JS
and PHP (although not perfect in some corner cases)

- added OC.Util.naturalSortComparator that uses the same algo that was
  used for the user list
- changed user list and files list to use OC.Util.naturalSortComparator
- removed toLowerCase() and changed the comparator to use
  String.localeCompare()
- added unit tests
- added OC_NaturalSort that is used by OCP\Util::naturalSortCompare()
Fixed sort algo for additional cases
Use afterBind to send fileId header for files and directories

afterBind is called for both files and directories and is now used to
send the OC-FileId headers.
make sure class file is loaded once
change logic in displayNamesInGroup and add some unit tests
Use Doctrine Platform to generate SQL query for table truncation.
Refactor internal session to write directly to $_SESSION
Update AWS sdk to 2.6.15
Fix failing AmazonS3::touch on updated aws sdk