xml template improvements

xml template improvements, taged properties (rl controller), title property

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation
- [ ] implement property title (translation keys) in content form
- [ ] change ResourceLocatorController in ContentBundle
- [ ] property access with tags


__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Tests pass?   | no => https://github.com/sulu-cmf/SuluTestBundle/pull/10
| Fixed tickets | none
| Doc           | none