Added canScroll and onClickListener options to Tooltip.Builder, and upgraded gradle build tools

[rjalmo]

This update adds two new options to the Tooltip Builder: canScroll and onClickListener. Getting the TextView object is also exposed as an interface method, so further customizations can be done after the tooltip is shown especially when clients provide a custom TextView via builder.withCustomView(). The gradle files have also been updated to 3.0.1 and compile with Java 8