Add a user preference for whether to automatically focus the input in mobile

[curiousdannii]

Soft keyboard will often take up to 50% of the available screen space, and in a game like City of Secrets where there are other windows, you can be left with only 30% of the screen for reading updates, just 8 lines.

It would be good to let the user choose whether the input should be automatically focused. Probably that means Quixe should have some kind of menu - maybe a partially transparent hamburger menu floating over the top? Could be hard because games don't expect that and might even put some input element in those places. The menu might need an option to hide itself.

[curiousdannii]

See erkyrath/glkote#9 for related discussion.

When a system like Voiceover is used it is important to keep the input element focused, so if we can detect Voiceover we should make sure the preference is automatically set.