IssueTracker

Component used: safe-args-gradle-plugin
Version used: android.arch.navigation:navigation-safe-args-gradle-plugin:1.0.0-alpha01

As the title says, the safe args plugin generates invalid code when argument names contain a period. I would argue that the plugin should generate valid code for periods. I've seen codebases that use class package names as part of the bundle key. Sanitizing the names to replace period with an underscore would allow for easier migration to the Navigation Component.

Some code samples:
```
    <fragment
        android:id="@+id/firstController"
        android:name="com.bluelinelabs.conductor.demo.controllers.ArchNavigationDemoController"
        android:label="ArchNavigationDemoController1">
        <argument android:name="NavigationDemoController.index" android:defaultValue="0" app:type="integer"/>
    </fragment>
```

```
  public int getNavigationDemoController.index() {
    return NavigationDemoController.index;
  }
```

```
public static ArchNavigationDemoControllerArgs fromBundle(Bundle bundle) {
    ArchNavigationDemoControllerArgs result = new ArchNavigationDemoControllerArgs();
    if (bundle.containsKey("NavigationDemoController.index")) {
      result.NavigationDemoController.index = bundle.getInt("NavigationDemoController.index");
    }
}
```