Fixed parseQueryString to handle empty values and plus signs

- now correctly parse query strings with '+' signs
- empty values are now parsed either as null or empty string
- added unit test for parseQueryString()
Files, trashbin, public apps use ajax/JSON for the file list

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