fixes download issue introduced by #10755

Conflicts:
	apps/files_sharing/public.php

When downloading a folder called "0001" PHP should fallback to parsing
it as string and properly detect that it is not a JSON array.

Fixes https://github.com/owncloud/core/issues/11012

maintain deprecated \OC::$session when getting or setting the session via the server container or UserSession

restore order os OC::$session and OC::$CLI

remove unneded initialization of dummy session

write back session when $useCustomSession is true

log warning when deprecated app is used

- fixed upload and storage statistics
- fixed infinite scroll to use the correct contain for scroll detection
- fixed unit test that sometimes fail for rename case
- controls are now sticky again
- fixed selection overlay to be aligned with the table
- fixed "select all" checkbox that had id conflicts
- fixed public page
- fixed global actions permissions detection
- fix when URL contains an invalid view id
- viewer mode now hides the sidebar (ex: text editor)
- added unit tests for trashbin
- clean up storage info in template (most is retrieved via ajax call now)

- FileList is now an instantiable class
- FileActions is now in namespace
- added App class for trashbin app
- moved trashbin overrides into classes extending FileList
- replaced many static calls with "this." or "self." to make the classes
  reusable/extendable
- new URL parameter "view" to specify which view is shown, for example
  "files" or "trashbin"
- added OC.Util.History utility class in core for handling history
- moved URL handling/routing to OCA.Files.App
- popstate will correctly update the current view and notify the view of
  the URL change so it can update the current dir
- added JS unitt tests for the trashbin app
- fixed public app to work with the new namespaces

- moved the summary code into a new class FileSummary
- FileSummary is calculated only once, then updated with add/remove
- added new OC.Util namespace for JS utility functions

Files app:

- removed file list template, now rendering list from JSON response
- FileList.addFile/addDir is now FileList.add() and takes a JS map with all required
  arguments instead of having a long number of function arguments
- added unit tests for many FileList operations
- fixed newfile.php, newfolder.php and rename.php to return the file's
  full JSON on success
- removed obsolete/unused undo code
- removed download_url / loading options, now using
  Files.getDownloadUrl() for that
- server side now uses Helper::getFileInfo() to prepare file JSON response
- previews are now client-side only

Breadcrumbs are now JS only:

- Added BreadCrumb class to handle breadcrumb rendering and events
- Added unit test for BreadCrumb class
- Moved all relevant JS functions to the BreadCrumb class

Public page now uses ajax to load the file list:

- Added Helper class in sharing app to make it easier to authenticate
  and retrieve the file's real path
- Added ajax/list.php to retrieve the file list
- Fixed FileActions and FileList to work with the ajax list

Core:

- Fixed file picker dialog to use the same list format as files app

OC_Util::setupFS($user) will create a data dir for the given string - no matter if the user really exists - OCP\JSON::checkUserExists($owner); introduces a ready to use check which will bail out with an JSON error

isPreviewAvailable wasn't always set as the files formatting code is
slightly different than the one from the files app.

Fixes #6423

necessary for https://github.com/owncloud/apps/pull/1476

Fixes #5534

Added missing condition to check whenever allowed zip size is unlimited.

Fixes #3717

 * Works in IE8, 9, 10, Firefox 24 and Chromium 30
 * Credits to Julian Müller @Julian1998

when _ is left in namespace and files are named after their classes the autoloader will also find classes in the lib folder of an app
its magic!