Create no-halo shields for bike routes

[nvkelso]

The existing bike route shields use the SDK icons which have solid color and then a ring of semi-transparent color. This muddies up the design.

Let's create new fully solid icons, and source from those instead for bike shields.

(The same new asset should be re-use-able for transit line shields.)

[nvkelso]

Basic styling is done.

But we should make the shields a little smaller, especially at zooms less than 18.

[nvkelso]

This is done.