#2427 Launcher UI tweaks

[Slawek Mikula]

Testing 2020.3.3 (AppImage, only running UI). Small UI nitpicks:

• additional scenery information - needs more padding (translated text overflows) - see additional_scenery-padding.png
• addons detail - needs resetting the scroll position - see movie addons-details-scrolling.mp4 (best to describe). Anyway it can be in other areas as well (but aircraft details does not show this)
• AppImage (and normal version also) - when there is no FGHOME (~/.fgfs) the data are initialized and the default size of the launcher (at least for me) have more 'portrait' than 'landscape' orientation. I've always resize it to more horizontal layout. See screens launcher_default_size.png, launcher_default_size_2.png. I think it should be laid in more horizontal orientation see launcher_my_size_heh.png - see aircraft description.
• don't know if it is only my (qt?) issue but the history buttons always are too tight aligned to the border. I think this is not as always have been because i saw it with more right padding somewhere. This is default after new AppImage run. See launcher_icons_padding.png

Anyway, these are only a very minor issues, but reporting anyway