Feature request: Data sync for ttsu

[kimjongbing]

On ttsu reader you can link up to something to sync your reading progress. In immersion reader (I think) you can't hook up to this so you can't sync across devices.

Unsure if it has not been implemented due to oversight, not being possible due to ios restrictions, or it is implemented and I just have missed it.

[mathewthe2]

This is on the backlog, but postponed until the data migration from the indexed-db in the browser to embedded sqlite is complete. https://github.com/mathewthe2/immersion_reader/issues/33