Webclient: Fix DOM based topic rendering (#505).

- Move cluster works
- Retype topic works
- While drawing an association topics can be crossed
- Remove topic highlight when an association is selected
- Set topic color works (Box Renderer Plugin)

View Customization Framework:

- new hook (Canvas & HTML):
{{{
update_view_properties(topic_view)
}}}
Used by customizer to update the rendering once custom view properties have changed.

See #505.
Merge branch 'master' into pax-web