Show helpful UI when landing on a drawing/splash page (for mousedrag and WASD controls)

[cvan]

I've seen more than a few tweets about folks getting confused when they land on a drawing.

They don't know about the mouse-drag (hovering over the grabbing isn't obvious enough IMO; and that's the fault of the cursor styling by the OS/browser IMO). And, even more commonly folks seem to not know about movement using wasd-controls (unless you're a gamer or been to an A-Frame scene before).

Given that the audience for A-Painter is quite wide, I think it'd be nice if we gave some nice visual hint with some text that disappears on mouse-drag (or a significant orientation change on mobile or upon the first drag-like touch gesture).

I was thinking something like this for the look-controls bit:

And, to indicate WASD, I can imagine something like the treatment of the arrow keys on this site (and they could disappear too, but that I'd say could be optional; the visual feedback could feel kind of nice):

I know A-Frame itself could benefit probably benefit from some UI when the look-controls and wasd-controls are shown, but I'll refrain from filing an issue there. I think perhaps introducing it here in A-Painter first could be a nice experiment.