Add More Keywords to Section Fronts

This makes non-facia section fronts consistent with facia pages, so that ads work.
Eg global-development-professionals-network/malaria-consortium-partner-zone
![image](https://cloud.githubusercontent.com/assets/1722550/4717421/d4411b9e-5914-11e4-93c8-ac4160104e55.png)


Feel a bit uneasy about this as it could end up stripping multiple parts of the page ID. I don't think any of our tag ids start with an edition string, so it ought to be OK ... but it might be simpler to just do 

```scala
val editionStrings = Edition.all.map(_.toLowerCase).toSet

val parts = pageId.split("/").toList match {
  case edition :: rest if editionStrings.contains(edition) => rest
  case x => x
})

// ... 
```