Updated Readium version

[nunommts]

What's this do?
This PR updates the app to support the latest version of Readium

Why are we doing this? (w/ JIRA link if applicable)
There's a feature request to update the Readium version

How should this be tested? / Do these changes have associated tests?
Open the Palace app
Open any Ebook
Confirm everything is working
Return and open any PDF
Confirm everything is working

Dependencies for merging? Releasing to production?
This PR also needs to be merged

Have you updated the changelog?
Yes

Has the application documentation been updated for these changes?
No

Did someone actually run this code to verify it works?
Tested by @nunommts

[io7m]

This looks fine to me, but I must admit that I have no idea what's going on with our PDF support. How is Readium involved? I thought we used some other third party library.

[nunommts]

@io7m We're using their PdfParser file. One of the main changes between the previous Readium version and this one is that the PdfParser now doesn't accept a constructor with no PDFFactory argument that would use their "default" document factory, so I had to import the code they're using on it.