Fix issue #3656 - Added fallback to 2D CSS transforms (offcanvas)

Opera 12.16 browser (Presto engine) doesn't support 3d CSS transforms.

This fix provide 2d fallback for 3d transforms.

Strange, but the translate3d mixin:

```scss
@mixin translate3d($tx,$ty,$tz) {
  // ...
  transform: translate3d($tx,$ty,$tz)
}
```
really used only for the 2d transforms

```scss
@mixin left-off-canvas-menu {
  // ...
  @include translate3d(-100%,0,0); // $tz always zero
  // ...
}
```

How about change tranlate3d, to translate?

```scss
@mixin translate($tx,$ty) {
  // ...
  transform: translate3d($tx,$ty)
}

@mixin left-off-canvas-menu {
  // ...
  @include translate(-100%,0);
  // ...
}
```