Is your feature request related to a problem? Please describe.

Related to the issue I raised on the Plover Python dictionary last time.

Sometimes some dictionaries are slower to load than the others, and it would be useful to have a visual indicator to know which one is slow.

Describe the solution you'd like

Make Plover show the "refreshing" state for only the actually-loading dictionaries on startup, instead of all of them.

Currently if a single dictionary is added, only that one has the refreshing state, which is desired. But on startup the refreshing icon only disappear when all dictionaries finished loading.

Implementation note: This might need some refactoring, because currently there's only the dictionaries_loaded hook triggered when all the dictionaries are loaded.

It's possible to trigger the hook when not all dictionaries are loaded, but (it breaks backward compatibility and) currently the hook is triggered inside engine, it would require some changes.