Emit events on _translate as well

[osartun]

This closes https://github.com/cubiq/iscroll/issues/1217

When using the keybindings option and controlling the slider with the keyboard _translate is used instead of _animate. So far _translate didn't fire any events. That caused inconsistencies: I had probeType = 3 to get a pixel precision feedback about every movement of the slider. But by using the keybindings option I could move the slider without my listeners being called.