Adapt to current Webclient: topic_dom signature.

Fix: icon scaling is performed properly when a topic is retyped and the new type icon has another size than the previous one.

Code cleanup.
Adapt to Webclient: rename view hooks.

- update_topic()           -> on_update_topic()
- update_view_properties() -> on_update_view_properties()
Fix: mini icon DOM coordinates are integers.

No float values.