Add Gradle quickstart for start.vertx.io

[codepitbull]

Description

We need to provide a Gradle-quickstart to make it easier for new users to start using vertx-scala.

Acceptance criteria

A full Gradle-Vert.x-Scala-project can be generated on start.vertx.io

[oliver-brm]

Looks like Scala does intentionally not appear there, see vert-x3/vertx-starter#118. I'll reach out to understand more about Vert.x QuickStarts.

[oliver-brm]

See vert-x3/vertx-starter#626

[oliver-brm]

See vert-x3/vertx-starter#626