boot.js: minor refinements of Google layers
boot.js: minor refinements of Google layers

- maxZoom is 21 by default after v0.10.0
- add  missed styler for default ingress map: https://github.com/IITC-CE/ingress-intel-total-conversion/issues/163#issuecomment-492187858

McBen/ingress-intel-total-conversion,sndirsch/ingress-intel-total-conversion,sndirsch/ingress-intel-total-conversion,sndirsch/ingress-intel-total-conversion,McBen/ingress-intel-total-conversion,McBen/ingress-intel-total-conversion,McBen/ingress-intel-total-conversion,McBen/ingress-intel-total-conversion,sndirsch/ingress-intel-total-conversion,sndirsch/ingress-intel-total-conversion