Make Component Manager accessible as a Component Script Service

Currently users have to do this:

{{groovy}}
import com.xpn.xwiki.web.Utils
def converter =  Utils.getComponent(Converter.class);
{{/groovy}}

When this is implemented they'll be able to do:

{{groovy}}
def converter =  services.component.componentManager.getInstance(Converter.class)
{{/groovy}}

This has 3 advantages:

• Uses the new way, i.e. Script Services accessible through the "services" variable
• No need for import
• Don't use old API's in the com.xpn package