ENH: consider images inside PDF made with onlyoffice

[0xNath]

closes #2613

Added code to detect patterns in "_get_ids_image". To avoid any conflicts with images that could be located directly in a page or images using the same ID in different patterns, images ids under patterns are returned in this form : "/Pattern/patternNameHere/imageNameHere"

Added code to deal with Pattern images in "_get_image".

Added a new test to verify ids and image data returned related to the modifications done above.