Turning off AF behaviour

[BastelPichi]

When turning off autofocus, before #80 the autofocus was locked to the current focus point.
However, on the new app versions, the focus point is hardcoded to the lowest focus point the camera supports. This is unexpected and unuseable on most phones.

Id be nice to have the old behaviour again.

[raphaelm]

I think we did not keep the old behaviour because it wasn't possible. I remember spending a lot of time on that topic. Happy for PRs that prove me wrong ;)

[BastelPichi]

This is indeed difficult. Setting AF Mode to IDLE does work on some devices, however it simply has no effect on others.

Maybe it would be an idea to allow the user to specify the focus point via a slider (either in the settings, or one that appears once you turn AF off)?

[raphaelm]

I don't think many people will be using that slider, but if you have a good idea how to place it unobstrusively, we'd be happy to look at a PR :)