The glue code context does not require an active scenario. As a result
it was possible to create scenario scoped beans that would be shared
(leak) between scenarios.

An example of this is illustrated below. Because this does require
access to the `GlueCodeScope` it is not possible to do this in
practice.

```java
@configuration
public static class TestApplicationConfiguration {
    @bean
    public BeanFactoryPostProcessor beanFactoryPostProcessor(){
        return factory -> factory.registerScope(SCOPE_CUCUMBER_GLUE, new GlueCodeScope());
    }

    @bean
    public ExampleService service(ScenarioScopedApi api) {
        return new ExampleService(api);
    }

    @bean
    @scope(value = SCOPE_CUCUMBER_GLUE)
    public ScenarioScopedApi api() {
        return new ScenarioScopedApi();
    }
}
```

However without registering the the `GlueCodeScope` at start up Spring
will complain about missing the cucumber-glue scope rather then
complain about scope not having started or the missing proxy mode.

So to avoid further confusion:

1. GlueCodeContext will check if the context has been started.
2. Add a `@ScenarioScope` annotation that sets the correct proxy mode.
3. Do some renaming of internal classes
4. Use a global counter for conversation ids

Related
 - #1970
 - #1667