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           | 

Should `"sulu/test-bundle": "dev-feature/node-helper"` not be merged upfront?