EPUB ReadingSystem object not supported

[rkwright]

The EPUB Reading System object does not appear to have been implemented.

Steps to reproduce:

1. Download EPUBTEST 0102 - Scripting Tests
2. Open in the app
3. Navigate to the "Reading System Object" section.
4. Run the tests

They all fail.

Tested with build 1.0.3

[mickael-menu]

Superseded by #171