Added chain localizaton finder

- There are now two localization finders which handle when a webspace is
  present, and when a webspace is not present (as is the case with
  Snippets).
- The Chain localization finder will delegate to the appropriate finder.

- [x] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | (releated to snippets)
| BC Breaks     | no
| Doc           | 

Yet another argument to the `ContentMapper`. In theory however this allows us to remove both `internalPrefix` and `languageNamespace`. But there is currently a dependency on the `languageNamespace` variable from the `Ext` logic which prevents me from doing this now.