Hide more UI / tap to hide Chrome

* **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