Implement the display of pdf media type

[tommybuonomo]

Currently there is ImageDisplayable, VideoDisplayable, and WebDisplayable. Requires implementation of a PdfDisplayable

[loicortola]

Proposal:
consider a pdf as a multi-page media. Every pdf should be considered as a "slideshow".
How about DisplayTime? should be for one slide? or for the whole slideshow? (meaning displayTimePerSlide = displayTime / slideCount ?)

[loicortola]

Suggestion:
As a quick fix, might just consider swapping the content every displayTimePerSlide within the same fragment with the following page.