Force title property for templates

Merge together with https://github.com/sulu-cmf/SuluWebsiteBundle/pull/72, otherwise the websitebundle will fail

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | Every template definition must now contain a property named `title`, therefore the tag `sulu.node.name` is not necessary anymore
| Doc           | https://github.com/sulu-cmf/sulu-docs/commit/536abca24d81a9cc4d1860ef5f177e58734a482f
I don't think so. Its not a client issue. We just need to namespace system properties ("structure" properties could remain without a namespace and/or have a configurable namespace).

We would just need to run a migration (we could save all such migrations for a major release).

But I think it is really bad to have both system and user properties in the same namespace -- this will break things eventually.