feat(insights): replace fixed overviews with a single arrangeable overview

Categories, Tags and Entities Overview are merged into one Overview page.
Levels are chips that can be dragged (or moved with the arrow keys) to set
the hierarchy and clicked to switch off, so any ordering of the three is
reachable from the same page.

Only the results reload on change; the controls stay in place. The chip
order is kept in the session and defaults to categories by tags, matching
the old Categories Overview.

app/apps/insights/urls.py

@@ -30,19 +30,14 @@ urlpatterns = [
         name="category_sum_by_currency",
     ),
     path(
-        "insights/category-overview/",
-        views.category_overview,
-        name="category_overview",
+        "insights/overview/",
+        views.overview,
+        name="insights_overview",
     ),
     path(
-        "insights/tag-overview/",
-        views.tag_overview,
-        name="tag_overview",
-    ),
-    path(
-        "insights/entity-overview/",
-        views.entity_overview,
-        name="entity_overview",
+        "insights/overview/results/",
+        views.overview_results,
+        name="insights_overview_results",
     ),
     path(
         "insights/late-transactions/",