SwiftUI: Open a book on tap

[gatamar]

This PR aims to open a book somehow.

Changes:

• extracted new services BookOpener, BookImporter , BookRemover from the LibraryService
• added a wrapper over the ReaderViewController
• improved navigation - when we open a book, a bottom tab bar disappears
• refactored Container, as now it has more responsibilities

Out of scope (coming soon in the next PRs):

• Highlights, Search, and any other Reader supporting views