auto option for backLabel

[wbyoko]

I added this in some code i'm writing, so i wouldn't have to pass around escaped titles throughout the application.

This is just a suggestion.

in ViewNavigator.prototype.replaceView
...
if (viewDescriptor.backLabel == 'auto') {
viewDescriptor.backLabel = this.history.length > 0 ? this.history[this.history.length-1].backLabel : null;
}
this.history.push...

in ViewNavigator.prototype.pushView
...
if (viewDescriptor.backLabel == 'auto') {
viewDescriptor.backLabel = this.history.length > 0 ? this.history[this.history.length-1].title : null;
}
this.history.push...

Thanks for app-ui.