Revert "Use native keyboard events to fill inputs"

This reverts commit c7ba561411ac20b18014c4f612b2a1ecbd7ce581.

Conflicts:
	lib/capybara/poltergeist/client/compiled/node.js
	lib/capybara/poltergeist/client/node.coffee

The native implementation caused problems, see e.g. #176 and #223.

When PhantomJS upgrades the WebKit version we can try again and see if
those issues still occur.

Closes #176, #223.