[LeftNav] Support show LeftNav with wipe gesture

[ysmood]

Such as wipe from screen's left edge to show LeftNav.

[pomerantsev]

I implemented swipe to close functionality, and I can make this work as well if people are interested. @ysmood, are there any other material design libraries doing it?

[cgestes]

interested, can you provide a PR ? :)

(I would like it to works for opening in some cases too)

[pomerantsev]

I can try to implement this during weekend.
There should probably be some restrictions.
Like only allowing this behavior when visual viewport width equals layout viewport width (which means that you can't scroll horizontally).
There's also a corner case when there are two or more nav components on the screen - we'll have to deal with this somehow.

[pomerantsev]

@ysmood, @cgestes can either of you guys test my implementation and say if that the way it works feels fine to you?
This PR might also benefit from a code review, so feel free to comment.

[cgestes]

Looks better.

Some glitches:

• swiping on the body of my test project do not works. (at the bottom of the page)
• swiping to open the leftnav (enough to open it but not complete), then clicking on the AppBar (not the button) twice produce strange behaviors. (first time it close the appbar as expected, second time the appbar appear but should not!)

[cgestes]

Humm wait. not sure what I tried.

On master if I click anywhere on the webpage the LeftNav open. (on android)
and the swipping behavior does not work at all.

It's close to be unusable.