Fix Unbound Reference Warning

When starting you get the warning

```
    Could not bind a reference of component
ch.netcetera.eclipse.projectconfig.net.client. The reference is:
Reference[name = IProxyService, interface =
org.eclipse.core.net.proxy.IProxyService, policy = dynamic, cardinality
= 0..1, target = null, bind = bindProxyService, unbind =
unbindProxyService]
```

 * change the cardinality of the proxy service
 * get the `IProjectConfigurationService` lazy
 * make the `IProjectConfigurationClient` reference dynamic

Fixes #13
Merge pull request #20 from marschall/reference-warning

Fix Unbound Reference Warning