[FEATURE] added localized title to template

added localized title to template.

```xml
<?xml version="1.0" ?>
<template xmlns="http://schemas.sulu.io/template/template"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://schemas.sulu.io/template/template http://schemas.sulu.io/template/template-1.0.xsd">

    <key>template</key>
...
    <meta>
        <title lang="de">Das ist das Template 1</title>
        <title lang="en">That´s the template 1</title>
    </meta>
...
</template>
```

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [x] submit changes to the documentation


__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | no
| Doc           | https://github.com/sulu-cmf/docs/blob/master/detail-specification/300-webspaces/DET-301-template-architecture.md#template-example