Add ::placeholder data

Selector is a [candidate](http://wiki.csswg.org/spec/css4-ui#more-selectors) for CSS 4 selectors, is supported by all major browsers (Opera doesn’t support it until 15 version) and is very often used.

Filled the data accordingly to [post](http://blog.teamtreehouse.com/the-css3-placeholder-pseudo-element) and [stackoverflow](http://stackoverflow.com/questions/2610497/change-an-inputs-html5-placeholder-color-with-css).