Hide more UI / tap to hide Chrome

[cdrini]

• Why: Make reading on small screens easier
• Size: L (Will require rejiggering the UI (including lending bar) to be overtop of the book for smooth hiding)
• Priority: Med (A big issue when reading on mobile, but less elsewhere)

Proposed fixes:

• Scrolling down hides all chrome. To bring it back, scroll up.
  • Pro: This is how browsers work on mobile devices
  • Will require a decent rejiggering of the UI to make all the chrome sit overtop of the book so it can easily be hidden
• Tapping center of screen takes toggles chrome
• Have another full screen button

• [ ] #1273
• [ ] #1274