[fr] Add ability to show random dark/light backgrounds, perhaps by time of day

[Gitoffthelawn]

Currently, Bonjourr allows specifying Unsplash collections for the background image. This is a great feature.

I haven't thought through the following completely yet, but it's been on my mind, so perhaps we can brainstorm together. ❤️ What if Bonjourr included the functionality to view random Unsplash images based on the brightness of the image? The idea would be that the user could select only dark or light backgrounds, and have Bonjourr only display random backgrounds matching that brightness. The backgrounds would no longer be from a specific, small, collection.

If we want to get fancy, Bonjourr could be programmed to switch brightness at times selected by the user (or perhaps by latitude, but that's not always exactly what the user will want). For the truly fancy, we could allow the user to specify something like this:

05:00-07:59 Images with average brightness of 50%, and no peaks above 70%  
08:00-10:59 Images with average brightness of 60%, and no peaks above 80%
11:00-15:59 Images with average brightness of 70%, and no peaks above 100%  
16:00-17:59 Images with average brightness of 65%, and no peaks above 80%  
18:00-19:59 Images with average brightness of 55%, and no peaks above 70%  
20:00-04:59 Images with average brightness of 30%, and no peaks above 40%  

Of course, this is simply a possible ideal level of flexibility, as IIRC the Unsplash API likely is not quite this advanced. But the overall idea is what I'm interested in discussing.

BTW, if the Unsplash API is too limited, Bonjourr could request multiple low-resolution backgrounds, perform it's own image processing on those low-res images, select the closest matching image, and then request a higher resolution version of the desired image.

Related: #493 (comment)

[victrme]

We were thinking of doing something similar in issue #94 !

There is a daytime function in Bonjourr that dictates when to choose morning, day, evening, and night for different features. It would be nice for the user to be able to assign different time of day to their images or collections.

Currently reworking the background feature and adding tons of new options, we'll see if this feature is doable !