Improve how controls are shown when you start reading

[seanredmond]

When you enter the webreader, the controls are visible, and continue to be visible unless you actively dismiss them. This gives the impression that they're persistent when they really aren't. I can imagine a few ways to improve this, but I'm not sure what is best:

• don't show the controls by default
• close them once you've picked something from the TOC
• close them when you tap left or right, in addition to center.

[aslagle]

I prefer the first option, but if we don't have any tutorial I'm concerned people won't realize they can tap to bring up the controls.