Add highlight annotations to ebooks

[MxMarx]

This pull request adds the ability to highlight and save text in epubs. Saved bookmarks reuse the existing "search book" ui.

To accomplish this, I used the existing bookmark schema, with the time property storing the CFI of the highlighted text. This posed a dilemma if a library item has both an audiobook and an ebook because they share the same id, so I extended the bookmark schema and api with a type property, which defaults to audio. This could cause problems if the ebook file changes after bookmarks are added, but that could probably be solved with some type of fingerprinting.

resolves #1558 resolves #1709

Should be compatible with #2584, but if not, I'll resolve any conflicts.

[Hutch79]

Hey, quick question, What's the state of this PR?

I found this PR a while ago and was looking forward for it to be merged.