Add brightness controls to persistent notification

[rieje]

Just a simple feature request--persistent notification and/or widget to quickly manually control brightness settings like f.lux. What I like about it (the way f.lux does it) is:

• Quick and predictable way of controlling brightness. Most situations is screen brightness is too low to see anything when I'm in broad daylight and I need to blindly change the brightness as I can't see anything. A persistent simple control for brightness via notification drop-down is useful in this regard. With f.lux, I can wake my screen, type my pin, dropdown the menu, and adjust the brightness as if my eyes are closed.

• Using incremental changes to brightness, as opposed to using a slider. Setting brightness should be quick and accurate (e.g. I know when I'm in a room vs. going outside I need to tap the brightness 5 times to increment/decrement by 50%)--the user shouldn't have to fidget to adjust the brightness to an accurate level when the environments he is in is nearly always the same (for me, it's: dark room, car, broad daylight, and the office).

[smichel17]

We do already have a persistent notification when Red Moon is active. It's a bit crowded, since it already has controls for changing the active filter; excluding the current app from filtering (if you use that feature) or pausing (if not); and turning off the filter.

I think the notification overall could use a redesign, since the current "excluded apps" feature is somewhat complicated to use. However, I want to do #122 first, since how we handle dimming will have a big effect on what controls we should have. I'd love to add a control something like Night Screen, where you can see other open apps while you're adjusting it.

[smichel17]

…if you're talking about a notification that persists even when Red Moon is not running, that's out of scope for this project, which is an "Android screen filter app for night time phone use."

[smichel17]

Closing in favor of #294