* Add commands to manipulate entry attachments from the CLI
* Closes#4462
* Add the following commands:
attachment-export: Exports the content of an attachment to a specified file.
attachment-import: Imports the attachment into an entry. An existing attachment with the same name may be overwritten if the -f option is specified.
attachment-rm: Removes the named attachment from an entry.
* Add --show-attachments to the show command
