MVP "spinner". Still needed: actual spinning, placement, etc
add loading indicator to initial species load;

remove indicator from xhr callback
remove unneeded let-binding
separate “spinner” from overlay
SHTYLIN
Fix spacing
make bg transparent, looks less disruptive that way

We still need the overlay to prevent user clicks on the UI when loading.
Merge pull request #26 from neo/spinner

Spinner (**rebases spinner branch**)