Prefix handlers keep a ConfigurationSource component around

Currently, URL prefix handlers access a ConfigurationSource component whenever a value is needed. The ConfigurationSource component is kept around in a private field. This is bad, because if the ConfigurationSource is or needs to be reloaded, things might break. In the hope it will make things more robust and less prone to issues, especially when components are reloaded, we ought to eagerly read the whole configuration when initializing a URL prefix handler and stop keeping the ConfigurationSource component around