Add scrollTo method

[mbardelmeijer]

Re-submission of #367.

When using click on elements which are not in the viewport, it's quite handy to add a simple scrollTo call to ensure the browser has the element in the viewport. We macro this in all our projects, but would be nicer to have support for this in the core.

Example:

$browser->visit(route('overview'))
   ->scrollTo('@create')
   ->click('@create')