Upgrading: Well the extension upgrade itself went smooth but project wise I wasn't aware at first there was any upgrading needed. Right clicking the Thunder theme still uploaded the themes to the project. Only after accidentily clicking the thunder explorer I was presented with a message that the installed Thunder Module wasn't updated. Perhaps after the next update a redirect to an 'upgrade documentation/release page' instead of the standard documentation would be best cause it was only by accident I discovered the 'register widget' icon on the Solution Explorer as well. So I went ahead and chose 'Install Sitefinity Thunder Module' which only worked on my remote site and not my working copy solution. (Maybe this is because I keep the .config files as a seperate project in the solution?) And manually had to copy/paste back the changes into my working copy. Error message: thunder.svc not found. Manually browsing through the Sitefinity error.log gave me this:
Type : System.ServiceModel.EndpointNotFoundException, System.ServiceModel, Version=18.104.22.168, Culture=neutral, PublicKeyToken=b77a5c561934e089
Message : The service '/Sitefinity/Public/Services/Thunder/ThunderService.svc' does not exist.
Source : System.ServiceModel.Activation