Backdrop with NavigationRail

[daadu]

Is your feature request related to a problem? Please describe.
Material Design Guideline have come up with a new component called NavigationRail which have explained its behaviour with backdrop (Check Backdrop section in the Guideline).

Describe the solution you'd like
The NavigationRail should rest on backLayer when backdrop is active (backLayer is visible) as shown in the picture in guideline

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Refer: #34

[daadu]

@WieFel Let me know your views on it.

[WieFel]

Interesting!
As far as I can see, NavigationRail is aimed for tablet/desktop sized screens, or am I wrong?
I think we could include it in the future, but I would suggest to do that after v1.0.