Check uploaded (content) files

Files uploaded through the AJAX endpoint (images, video etc.) need to be check whether they are valid:

• the extension must be in H5PEditorConfig.contentWhitelist
• the file must be smaller than H5PEditorConfig.maxFileSize
• the package it is added to must not have a greater total size than H5PEditorConfig.maxTotalSize

There are further checks in h5p-editor-php-library:h5p-editor-file.class.php:

• check if field type & mime-type match
• check if mime-type is allowed
  • if image (check by mime type): - only allow png,jpg,jpg,gif - read image (& get file size)
  • if audio (check by mime type): only allow mpeg, mp3, m4a, mp4, wav, x-wav, ogg
  • if video (check by mime type): only allow mp4,webm, ogg
• check if mime-type matches extension