prop getActions return functions to execute action

[esganzerla]

This includes the prop getActions, which will return to a function a json to execute _forceRightSwipe, _forceLeftSwipe and _forceUpSwipe.

The return looks like:

{
  yup: this._forceRightSwipe.bind(this),
  nope: this._forceLeftSwipe.bind(this),
  maybe: this._forceUpSwipe.bind(this),
}

It can be used like:

render () {
  let swipeActions
  return (
    <View>
      <SwipeCard getActions={actions => { swipeActions = actions } />
      <TouchableHighlight onPress={() => swipeActions.yup()}>
        <Text>EXECUTE YUP ACTION</Text>
      </TouchableHighlight>
    </View>
  )
}

This probably helps on Issue #62.

Note: I took the liberty to include the swipe as using on PR #70. It's easy to remove if not approved.
Note 2: I took off the function () => { alert('tapped') } from default prop onClickHandler. Seemed as possible problem someone might have.

[esganzerla]

Should we close this PR?