Fix missing parens in calls to extracted methods with empty parameter lists

This PR addresses an issue reported in scala-ide/scala-ide#686 by @huitseeker:

```scala
class ExtractorTesting {

  val major: Int = 1
  val minor: Int = 2
  val patch: Int = 3

  major * 100000 + minor * 10000 + patch * 100

}
```

Should give me

```scala
class ExtractorTesting {

  val major: Int = 1
  val minor: Int = 2
  val patch: Int = 3

  extracted()

  def extracted() = {
    major * 100000 + minor * 10000 + patch * 100
  }
}
```