Emulated click events on mouse devices

The map already emits emulated `click` and `dblclick` events on touch and pointer devices. With this commit the map emits emulated `click` and `dblclick` events on mouse devices as well.
Emulate click events only on mouse "action"

`click` events are fired only if the mouse action button is pressed. This prevents `click` events from being fired when the middle mouse button is used.

Also, without this commit, in Chrome with emulated touch events enabled, double-clicking the map doesn't zoom the map. This is because `ol.BrowserFeature.HAS_TOUCH` is `false` in that environment. The commit fixes it by testing `isMouseActionButton` on mouse devices only.
Remove unused ol.MapBrowserEventHandler#relayEvent_ func
Remove mousedown listener on first touchstart
Add tests for emulated clicks
clickOnly condition checks map clicks
Map "click" event renamed to "singleclick"

As discussed with @tschaub in #1195.
Merge pull request #1195 from elemoine/click

Emulated click events on mouse devices