PanoMarker: adding support for browsers other than Chrome + small fixes.

* Non-Chrome browsers fall back to a simpler rendering which is just
  panning the raw StreetView tiles - this is being considered now.
* Redrawing the Marker when zoom level changes
* Fixing linter warnings

Functionality tested in Chrome 39+, Firefox 33+, Safari 8.

Signed-off-by: Martin Matysiak <marmat@google.com>