Saved tab in library

[spacedmonkey]

Summary

Currently the last saved tab doesn't work for unsplash tabs. This PR fixes that and by saving the setting under a new key, so it doesn't break anything.

Fixes UVP-189

Checklist

• [ ] My pull request is addressing an open issue (please create one otherwise).
• [ ] My code is tested and passes existing tests.
• [ ] My code follows the Contributing Guidelines (updates are often made to the guidelines, check it out periodically).