First version of the zoomslider control.
meld me
Merge branch 'zoomslider-own-ui' of https://github.com/marcjansen/ol3 into zoomslider-own-ui

Conflicts:
	css/ol.css
	examples/zoomslider.html
	examples/zoomslider.js
	src/objectliterals.exports
	src/ol/control/zoomslidercontrol.js
	test/spec/ol/control/zoomslider.test.js