Add this extension to the Zikula Extension Library

#### Hi @craigh!

You requested to add this extension to the [Zikula Extension Library](http://zikula.org/library/) :star:. You're just two clicks away from there:
1. Merge this PR!
2. Add a new Tag as version 1.0.4 (either using the git command line, your favourite git client or the [GitHub online interface](https://github.com/craigh/Demo/releases/new))!

In case something doesn't work as expected, feel free to open an issue in the [Extension Library repository](https://github.com/craigh/ExtensionLibrary/issues/new)!
@cmfcmf - do you know why this is replacing with 4 backslashes? I assumed that php escaped the first so, the code is
```php
$class = str_replace("\\", "\\\\", $extension['namespace']);
```

is the var pulled from the request already escaped? (e.g. `$extension['namespace'] = "Zikula\\Module\\DemoModule"`)