Combine two normal tile buckets

[meetar]

For now the two dev urls are each only serving half of the desired tiles – there's a way to combine them using a shader, which is ~simple when you just want to display the tiles, but more complex when you want to use the result in other shaders. I wasn't able to get this working properly today – I'll try again when I get the chance.

[nvkelso]

Thanks!

(This will be for debug only during dev. Once prod tiles are available, we'll switch back to using a single source.)

[nvkelso]

Not to be fixed.

[meetar]

Yeah as far as I can tell this would have required duplicating every style, which wouldn't be practical in this case.