implement full-page screenshots for webkit browsers

[skwakman]

Webkit browsers such as Chrome, Safari and Opera don't produce full-page screenshots in Selenium. Until this is finished (which doesn't look like it happen soon: https://code.google.com/p/chromedriver/issues/detail?id=294) VisualReview-protractor should implement a commonly used workaround: scroll the viewport, make screenshots along the way and stitch the screenshots together to fake a full-page screenshot.

[monkpit]

@skwakman the discussion for this issue mentioned an experimental fix might be released "in a couple of weeks" - was this ever implemented? I wasn't able to tell after reading the discussions.

[wlsf82]

Seems that now this happens with Firefox (v61.0.1) as well :(