TISTUD-6877

TISTUD-6877 NPE in Log when Studio is shutdown

- guard against null (which shoudl only happen when we're trying to log an analytics event while the platform is shutting down and usage plugin has already "stopped").
- extract and interface for StudioAnalytics
- deprecate StudioAnalytics.getInstance, the plugin should manage the lifecycle of the instance.
- Callers should do UsagePlugin.getDefault().getStudioAnalytics to grab instance, hiding bheind interface. They should deal with potential null ref to plugin since it may be shutting/shut down.

Basically I don't think we have any way of properly dealing with the veent we're trying to send in a case like this, we basically just drop it.