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

test/models/time_series/trend_test.rb

@@ -0,0 +1,45 @@
+require "test_helper"
+
+class TimeSeries::TrendTest < ActiveSupport::TestCase
+  test "handles money trend" do
+    trend = TimeSeries::Trend.new(current: Money.new(100), previous: Money.new(50))
+    assert_equal "up", trend.direction
+    assert_equal Money.new(50), trend.value
+    assert_equal 100.0, trend.percent
+  end
+  test "up" do
+    trend = TimeSeries::Trend.new(current: 100, previous: 50)
+    assert_equal "up", trend.direction
+  end
+
+  test "down" do
+    trend = TimeSeries::Trend.new(current: 50, previous: 100)
+    assert_equal "down", trend.direction
+  end
+
+  test "flat" do
+    trend1 = TimeSeries::Trend.new(current: 100, previous: 100)
+    trend3 = TimeSeries::Trend.new(current: 100, previous: nil)
+    trend2 = TimeSeries::Trend.new(current: nil, previous: nil)
+    assert_equal "flat", trend1.direction
+    assert_equal "flat", trend2.direction
+    assert_equal "flat", trend3.direction
+  end
+
+  test "infinitely up" do
+    trend = TimeSeries::Trend.new(current: 100, previous: 0)
+    assert_equal "up", trend.direction
+  end
+
+  test "infinitely down" do
+    trend1 = TimeSeries::Trend.new(current: nil, previous: 100)
+    trend2 = TimeSeries::Trend.new(current: 0, previous: 100)
+    assert_equal "down", trend1.direction
+    assert_equal "down", trend2.direction
+  end
+
+  test "empty" do
+    trend =TimeSeries::Trend.new
+    assert_equal "flat", trend.direction
+  end
+end