Squashed commits from PR #4364 for master.

provide correct path for require_once

* owncloud/fix_4326:
  use __DIR__ instead of realpath
  provide correct path for require_once

use theme name and title for password reset

allow empty configvalue in appconfig

Use plural translations

Send mime-type for new files

Fix sharing defaults

Fix recursive scanner to reusing etags

Do not pass numeric strings to strtotime() when formatting dates.

strtotime() will return false and the date will be formatted as the 0-timestamp
(e.g. January 1, 1970 00:00) otherwise.

show 'More apps' link to app administration directly in app navigation

Plural translations

Move dbtype depending logic into object per type

oc_cache needs to disable file proxys for read/write operation.

General CSS cleanup

fix function call for searchUsers()