Set Mode in a logical order

The application mode is an Enumeration, which are ordered. However for Mode this order was not logical:

```
scala> Mode.Dev < Mode.Prod
res0: Boolean = true

scala> Mode.Test < Mode.Prod
res1: Boolean = false
```

Test should be less than Prod, so one could write code like:
```scala
object Global extends GlobalSettings {
  override def onStart(app: Application) =
    if (app.mode < Mode.Prod) { seedMockData() }
}
```