Global styles are not applied to SVG

[danielweck]

Readium supports applying global styles to documents so as to, for example, create night mode, etc. However, there is now way for such styles to be applied to SVG content, whether embedded or as a SVG spine item. As a result, effects such as night mode fail.

This applies to all platforms. iBooks has the same bug.

Bugzilla:
https://app.devzing.com/Readium/bugzilla/show_bug.cgi?id=67