Use setters and getters instead of observable as a function about lithium-ui

[Munawwar]

Hmm..When it comes to observable array, I cannot extend native JS Array, since I cannot let a user directly change array with square brackets (like in the example above, let user do this.list[0] = 'something'), because that change cannot be detected or overridden. Currently observableArray() returns a copy of the original array, hence change to it doesn't need to be detected.
So maybe I shouldn't make a change till Object.observe is supported in all major browsers?

[Munawwar]

Will look into this again when Object.observe becomes cross-browser.