Added nope/yep buttons

[davidyaha]

This PR is based on an old PR by @kn4rfy. I haven't included the back button like he did because it is of no use for me. My implementation adds custom render props to the swipe cards component.

Example Usage:

renderYupButton() {
    console.log("Rendering");
    return (
      <View style={[styles.roundButton, {backgroundColor: ColorConstants.emerald}]}>
        <Icon name="heart" size={35} color="white"/>
      </View>
    );
  }

  renderNopeButton() {
    return (
      <View style={[styles.roundButton, {backgroundColor: ColorConstants.darkishRed}]}>
        <Icon name="times" size={45} color="white" style={{paddingBottom: 2, paddingRight: 1,}}/>
      </View>
    );
  }

render() {
        return (
      <SwipeCards
        cards={this.props.cardDataList}
        renderCard={(cardData) => <Card {...cardData} />}
        renderNoMoreCards={() => <NoMoreCards />}
        handleYup={(card)=>this.props.onSwipe(card.id, true)}
        handleNope={(card)=>this.props.onSwipe(card.id, false)}
        showNope={false} showYup={false}
        renderYupButton={this.renderYupButton}
        renderNopeButton={this.renderNopeButton}
        containerStyle={styles.container}
        buttonContainerStyle={styles.buttonsContainer}
        loop={this.props.loop}
      />
    )

[davidyaha]

Hey @dcworldwide,

I've opened this PR on your fork instead of the source repo because it seems that this is the most updated and has allot more customization options.
Currently I am pointing my package.js config to my own repo but I would certainly prefer directing it to your repo instead. I also think that at this time, it might be worth declaring this as the official repo and publish to npm.

Thanks for the work done here! It was very helpful!