[WIP] xml template improvements

Implement missing XML Template Features, such as tags, title, multilingual flag: 

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation
- [ ] extend xml schema
- [ ] extend cache class gen
- [ ] tags parsing
- [ ] replace property access with tags
- [ ] implement mapper multilingual


__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | yes
| Fixed tickets | https://github.com/sulu-cmf/sulu/issues/76
| Doc           | <url to doc>