Allow the CSS URL for annotations to be set via reader_views updateSettings functionality.

The CSS can be set with annotationCSSUrl key:

    readium.reader.updateSettings({'annotationCSSUrl': '/asdfasdf/'})

Note this only works on the next iframe load.
Allow passing of the annotations css url in the constructor object.
Merge pull request #10 from dmitrym0/develop

Allow the CSS URL for annotations to be specified via an option has to the reader_view constructor