Support ES7 Object rest/spread properties

[mhegazy]

Here is the ES7 proposal:
https://github.com/sebmarkbage/ecmascript-rest-spread

Rest Properties

let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
x; // 1
y; // 2
z; // { a: 3, b: 4 }

Spread Properties

let n = { x, y, ...z };
n; // { x: 1, y: 2, a: 3, b: 4 }

[DanielRosenwasser]

Duplicate of #2103.