feat(protractor): allow advanced features for ElementArrayFinder

changed ElementFinder as a subset of an ElementArrayFinder.

This enables actions on ElementArrayFinders, such as:
`element.all(by.css('.foo')).click()`

The function `filter` now returns an ElementArrayFinder, so you may also do:
`element.all(by.css('.foo')).filter(filterFn).click()`

or

`element.all(by.css('.foo')).filter(filterFn).last().click()`

Author: hankduan