Synchronisation between views in Annotation Editor isn't reliable

[sdruskat]

The view synchronisation between the different views connected to the Annotation Editor in the Annotation Graph Perspective isn't reliable. This concerns the Annotation Editor itself, the Sentence View, and the Level View.

This produces weird errors, e.g.

• when creating new elements in the annotation graph, such as elements not appearing due to levels not being activated, etc.
• relations pointing into the upper left corner as their target node isn't available for anchoring.

This is a showstopper which must be fixed for 0.3.0, i.e., 1.0.