Added mdPreventRefocus in sideNav

[jaxoncreed]

The code here

material/src/components/sidenav/sidenav.js

Line 377 in 7c6ff36

if ( !scope.isOpen ) {

refocuses on the element that opened the sidenav. This functionality isn't desirable in every context (for example I have an element with a md-tooltip that opens a sidenav. When the sidenav is closed, the tooltip with show up because the opener has been focused on)

Now adding md-prevent-refocus="true" will prevent this behaviour.

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[devversion]

@jaxoncreed Thanks for the contribution - I will close this PR, because a more elegant solution is already pending. See #7965