[structure view] update catalog registry when classpath changes

[martinlippert]

The registry that looks up the stereotype definitions from the JSON files needs to update itself:

• changes on the classpath of the project (via project listener)
• changes to those files from the project itself (changes to files of this type from source folders)

This does not include the automatic update of the UI. That can be done by pressing the "reload" action on the UI. Since changes to those metadata files should not happen as part of the usual daily work, having no automatic UI update here should be just fine.

[martinlippert]

In addition to that, pressing the "reload" action on the UI should always trigger a reload of the metadata files as well. So that a "reload" really reloads everything and does not re-use certain pieces from internal caches.