Make the mobile version more equal to the desktop version

[goto-bus-stop]

We could start paying more attention to the mobile version by, for example, sticking all the desktop-specific stuff into a desktop/ subfolder instead of treating it as the "main" code and mobile as a secondary part.

Mobile should have at least:

• Playlist creation
• Media search
• A better settings layout (just needs some flexbox magic probably)

And more nice to have:

• Importing (actually pretty important but media search is even more critical)
• Media editing

When selecting a playlist to add media to, we can use the bottom sheet component instead of the popover list.

Also listing some tweaks from #1686 here for now, should move to its own issue later:

• The mobile loading screen has icons that look clickable, maybe hide them
• Use the current videoDisabled style also when nobody is playing (but with different text)