[Lens] Clean up range operation state handling

[flash1293]

The range operation ("Intervals" in UI) is currently reading a value from ui settings on first render of the UI, writing it into the persistent datasource state. This is happening to determine the default value for the granularity slider and to use the value for the first range when switching to manual intervals.

This has several problems:

• The behavior is only triggered if the UI is actually rendered, which is not always the case (e.g. if the user just drops a field without opening the flyout)
• Changing the ui setting won't be reflected in saved visualizations because they keep the old state around by themselfes

To clean this up, the following approach should be taken:
Do not update the state on first render, but keep the ui setting only in the local state of the UI and use it as a fallback if the datasource state value is still null. As soon as the user starts messing with the settings, use the value the user configured and save it in datasource state.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)