Linked maps example broken

[kylebarron]

Need to clean up view state handling

[keewis]

just to mention, linking view states is much better using ipywidgets.jslink (if that's the only thing we do), because that doesn't need to roundtrip to and from the kernel and thus doesn't have a lag between the linked maps.

For example:

map1 = ...
map2 = ...

ipywidgets.jslink((map1, "view_state"), (map2, "view_state"))