Fit the artworks to screen

[yellowbluesky]

A user has reported that on their very tall phone, landscape art does not look good requiring a lot of scrolling to see the entire artwork.

This could be implemented by somehow adding letterboxes or pillars to the artwork. I can override openFile() in PixivArtProvider, and apply the fitting there, thus preserving the original artwork.

I can take this a step further by adding a slider for how pillars the app should add. E.g. a slider maxed out would result in a tiny landscape artwork in the center of a portrait screen, which a slider halfway would result in the artwork occoupying mostly the center of the screen with some excess hanging off either side.

An issue would be if the user has rotation enabled on their home screens. I can provide only one copy of the artwork to Muzei (they keep its own local copy), so i can only provide one orientation of scaling