View screenshots in full screen

• F-Droid version (in the About screen): v0.103-alpha1

What did you do? (clear steps if possible)

Opened App Details for an app that has screenshots (e.g. any of the apps in the Guardian Project repository).

What did you expect to see?

Screenshots which you can scroll through, and the ability to view each screenshot in more detail.

What did you see instead?

While screenshots can be scrolled left to right correctly, users are unable to see them in more detail (e.g. full screen).

We should make it so that when a screenshot is touched or held, that it is shown in fullscreen. I'm not quite sure on the exact UX that this would entail, but happy to hear suggestions (ping @crwinfrey). I'm not sure how big each screenshot is expected to be (ping @eighthave). If they are not particularly high resolution (e.g. this screenshot) then perhaps it should not be full screen, but rather it should expand to take up most of the screen as a popup?

I'm assigning this to %0.104 right now, because %0.103 - UX Overhaul is starting to stabilize right now and we should probably focus mainly on regressions. Also, the screenshots support still works for the most part, and allows people to get an idea of what the app looks like even though they are quite small right now.

mentioned in issue #954 (closed)

@pserwylo I agree that tapping on a screenshot should make it go fullscreen. Tapping the hardware back button on the device would exit out of fullscreen, and return to the app details.

I think we should start with the easiest way to show the image as big as possible. Later on, I could see allowing the user to swipe through the screenshots when they are big. I think the screenshots will require having some kind of frame, if they were just simply made fullscreen, that would look like the active app.

changed milestone to %1.1