Added "type=text" makes it look like nice like all other fields

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

Changed jQuery selector for public preview to public_upload to correctly show preview

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

Fixes #6423

When a dir has no delete permission, the draggable isn't initialized on
files. This fix makes sure we don't try to destroy a draggable when it
wasn't inited in the first place.

Fixes #6254

- Refactored file tr lookup into FileList.findFileEl that uses
  filterAttr to avoid escaping issues in jQuery selectors
- Fixed versions and sharing app to properly escape file names in
  attributes

- L10N now converted to string to make them work with json_encode
- Added specific error message when server doesn't allow fopen on URLs
- Fixed client side to correctly show error message in a notification
- Added OCP\JSON::encode() method to encode JSON with support for the
  OC_L10N_String values

Added new OC\Response API called setContentDispositionHeader() that
contains the needed workarounds for UTF8 and IE.

Refactored download code to use the new API.

Removed unused trashbin download file.

fixes #6108