Replace onClick with onMouseDown

onMouseDown is actually triggered *before* blur in at least Firefox and Chrome. IE test is still needed.

This way we no longer need the ugly and flaky setTimeout (only one left to defer the focus for Firefox).
Found this suggestion at http://facebook.github.io/react/tips/communicate-between-components.html and I liked it! It seems similar to the following Coffeescript we use at HackerOne:

```coffeescript
handleClick: (item) -> =>
  @setState clicked: item
render: ->
  div onClick: @handleClick(item)
```

What do you guys think?