Add a `destroy` command

Ignite have a `generate` command which is producing an example file from plugin. The missing command is `destroy` which is remove a file that generated by the plugin. Not only add a new command, this will need to change the plugin behavior as well.

```
$ ignite g saga hello
✔︎ App/Sagas/HelloSagas.js
✔︎ Tests/Sagas/HelloSagaTest.js
$ ignite d saga hello
✘ App/Sagas/HelloSagas.js
✘ Tests/Sagas/HelloSagaTest.js
```

Start by tracing the existing `generate`/`g` command and the plugin behavior that creates the example files. Define how `destroy`/`d` should identify generated files, then verify the sample flow removes both listed files and reports the results shown in the issue.

Written by the indexing model from the issue text.