Add Implicits object to help datatable transformations

[gaeljw]

AIms to fix #56

Import the new Implicits object and benefit from conversions methods to Scala types on the DataTable type:

import io.cucumber.scala.Implicits._

Given("the following table as List of Map") { (table: DataTable) =>
  val scalaTable: Seq[Map[String, Option[String]]] = table.asScalaMaps
  // ...
}