ezmultiupload 6.1.0: the new upload page

The upload page is new in admin4, admin4l and adminui; the classic design/admin keeps the 6.0 page, which works
with the same server. Guide: doc/upload-page.md.

• Added: The page in the frame of the content action pages (box header, box content, control bar with the main
  action first) with the administration's shared controls; light and dark mode.
• Added: The target location with its path; Change location... opens a location picker; a queue row can have a
  location of its own; the last location is the eZPreference exp_multiupload_location.
• Added: Files, folders, drag and drop and pasted images; per file a preview, the class it becomes, an editable
  title, the alternative text of an image (required where the class asks), progress and status; cancel, retry and
  remove per row and for all; three uploads at a time; a summary toast.
• Added: Checks before anything is sent (ezmultiupload/service, Action=check): the create permission for the class
  in the location, the type list, the size limit (new MaxFileSize=64M and PHP's limits), the alternative text, and
  a file of the same name and size already there (skip, rename or upload anyway).
• Added: Keep as drafts; after the upload view and edit links, and Move to..., Add location... and
  Remove... (to the trash, confirmed) through the kernel's content operations and their permission checks.
• Added: Import compressed zip file(s) contents (off by default, eZPreference exp_multiupload_zip_import; off, a
  ZIP file is one File item): the entries are listed, can be unticked, and are imported with the folders kept as
  folder items or flattened (eZPreference exp_multiupload_zip_mode).
• Added: expMultiuploadZipImporter, a ZIP import backend with inspect(), extract() and cleanup(): entries by
  content type and class, nested ZIP files to MaxDepth, unsafe paths, links, devices, encrypted entries, ZIP bombs
  and disallowed types skipped with a reason, extraction with a byte budget into a private directory per call;
  [ZipSettings] gains MaxFileSize, AllowedMIMETypes[] and DeniedExtensions[] (see doc/upload-page.md,
  "ZIP import").
• Added: SVG images in galleries (*.svg, *.svgz), sanitized by the kernel, previewed from the stored file.
• Added: expMultiuploadService::canUploadAt(), one check whether the current user can upload at a node.
• Updated: "Upload multiple files" in the content tree works on every container (new AnyContainer=enabled); it used
  to end in the kernel's "object is not available" error on any location that is not a folder or gallery. A location
  that cannot take files shows the reason and offers the nearest one above. AnyContainer=disabled keeps the 6.0 rule.
• Updated: Every request that changes something is a POST with the session's form token (checked again in constant
  time), never accepted from another site; node ids are positive integers only.
• Updated: English and German texts for the new page.