Flashlight brightness control

[Riksu9000]

At first I was planning on fixing #702 a different way #735 (comment), but then I found that brightness control can actually be useful in pitch black #735 (comment).

This PR adds adjustable brightness control to the flashlight app. The default brightness level will be the current backlight level.

By default the flashlight will be off, so it won't blind the user on launch.

The brightness control affects the backlight while the flashlight is disabled, which should make the icon dim enough that it isn't an issue.

Also added swipe down to exit and changed return app to QuickSettings.

If we find that a red flashlight color is actually usable and beneficial in some use case, that could be added behind a long press.

After recording this video, I changed the opening animation to a slide up, like the other apps.

Fixes half of #702. Shake algorithm should be added later.

VID_20211013_125548.mp4

[geekbozu]

I quite like this, This also might benefit from #575 once that gets closer to completion!

[Itai-Nelken]

I have been using this pr for a few days, and it works great! the flashlight app is much more usable and pleasant to use.
A suggestion:
Usually when I open the flashlight app is because I want to use it, and the extra tap to turn it on is sometimes annoying.
I understand why it's good to have it open off, especially with the ghost touches issue. so maybe make it a setting (though the settings already feel cluttered on latest develop...)?

[JF002]

Awesome, thanks!

[medeyko]

It's great that the torch is now ajustable, but personally for me it has became much less usable.

I often use it to routinely light a room. For this I need a torch that lights at maximum level with minimum gestures.

The old version (firmware 1.6.0) required only TWO gestures: 1. swipe left for menu; 2. click on the torch icon.
Now (1.7.1) I have to make FIVE gestures: 1. swipe left for menu; 2. click on the torch icon; 3. swipe left to increase light; 4. swipe right to increase light; 5. click to turn the torch on.

This is quite inconvient. I would like to either have an opportuninty to set the default light level to maximum and the torch state to on, or have some other short sequence (of no more than two gestures) that allows to turn the torch on maximum.

Also it's a pity that requests to support RED color were rejected. There are lot cases when low-energy photons are preferable, like photograhy or astronomy. Also, the red color is used to draw attention. Namely, I would use red torch when walking by roadside. It might be just a fourth "light level" option, a red one after three white ones.

For the latter use case, it would be nice to have a strobe ligth option for (it draws more attention and conserves battery power), but probably it's another topic for discussion.

(Please point where to post my comment if I chose the wrong place.)

[Riksu9000]

@medeyko A new issue would be the best place to discuss this.