Set proper proxy theme

[di72nn]

There's that annoying activity switching animation when sharing to Shaalier if it doesn't display dialog (so there's no activity to switch to). This proxy theme removes the animation.

This works fine (used in wallabag android app for a couple of years already) if the window is guaranteed not to display any UI, but may have side effects if the activity optionally shows UI. I tested the dialog mode only on Android 9 - it works ok, but the activity switching animation was different (probably because of windowIsTranslucent).
Maybe having a separate activity that never shows anything would work better.

I figured you should know about it, even so this is not a proper solution.

[dimtion]

Thanks @di72nn great PR!

I've tried this out a bit, about the animation I don't have any strong stand on them, I did not work at all to have nice animations.

I'm not sure if you had the chance to test on a taller screen size, but tweaking a bit with you branch I had an issue at the the bottom of the screen where the underlying window would appear. This is a bit more worrisome than the animation, see the following screenshot:

[di72nn]

Yeah, that's problematic. I guess the only decent solution is to have one activity that never shows UI and delegate to another activity for UI.