Rename rpc methods to be more consistent

Between guests <-> sidebar
- `showViewer()` to  `showAnnotations()`
- `updateViewer()` to `updateAnnotations()`
- `toggleViewerSelection()` to `toggleAnnotationSelection()`

All these renames were to enforce encapsulation and these calls
are more like APIs. To guest side really do not have to know anything
what the sidebar has or does.