WORKFLOW-4: Merge error when publishing documents with FS attachments on 5.4.5
** Starting with this change the workflow is no longer compatible with versions < 5.4 **
* Moved dependency of publication workflow version 1.4 to XWiki 5.4.6.
* Removed the code handling attachments on publishing since the merge function of 5.4+ is also handling attachments (XWIKI-9120). Added a load attachments call, though, so that the merge can work properly with the prepared documents