VaultInk 0.57.0

Faster Search in Book (#24) and a plainer corner lock screen (#22).

• Search in Book reads each chapter's text directly instead of laying it out first, in small steps. Hits appear while it works, Back stops it at once and keeps what it found, and a hit shows "chapter name - N%" (the page when known).
• Corner lock: the screen shows only "Locked" and the owner's name and phone; the hint line and the corner marks are gone.

Tested in the simulator on a 120-chapter test book, not on a device. Full list: CHANGELOG.md.