[WCM] New Feature: Change the Default Command in the Console component

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#9776)
| Applies to    | 2.5+
| Fixed tickets | 

I followed the suggestion from @WouterJ in IRC on changing the `single_command_tool` and added the documentation for the new feature there.