[LeftNav] Fixed missing onNavOpen event.

[maoziliang]

Not trigger onNavOpen after swiping to open the LeftNav

[maoziliang]

This because the open state is not correctly set. We can not set open to true just for showing the overlay. Open or not hasn't become a reality.

[pomerantsev]

This seemingly simple component is becoming more and more convoluted, but this is a necessary fix if you support onNavOpen.
And I agree that #1222 should also be addressed - not everyone might need this behavior.

[hai-cea]

Thanks @maoziliang @pomerantsev