Add the ability to "rollup" values in a time series (#554)

* Clean up time series models

* Add value group rollup class for summarizing hierarchical data

* Integrate new classes

* Update UI to use new patterns

* Update D3 charts to expect new data format

* Clean up account model

* More cleanup

* Money improvements

* Use new money fields

* Remove invalid fixture data to avoid orphaned accountables

* Update time series to work better with collections

* Fix tests and UI bugs

app/views/shared/_trend_change.html.erb

@@ -4,7 +4,7 @@
   <% if trend.direction == "flat" %>
     <span>No change</span>
   <% else %>
-    <span><%= styles[:symbol] %><%= format_money trend.amount.abs %></span>
+    <span><%= styles[:symbol] %><%= format_money trend.value.abs %></span>
     <span>(<%= lucide_icon(styles[:icon], class: "w-4 h-4 align-text-bottom inline") %><%= trend.percent %>%)</span>
   <% end %>
 </p>