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/models/time_series/value.rb

@@ -0,0 +1,32 @@
+class TimeSeries::Value
+    include Comparable
+
+    attr_accessor :trend
+    attr_reader :value, :date, :original
+
+    def initialize(obj)
+        @original = obj[:original] || obj
+
+        if obj.is_a?(Hash)
+            @date = obj[:date]
+            @value = obj[:value]
+        else
+            @date = obj.date
+            @value = obj.value
+        end
+
+        validate_input
+    end
+
+    def <=>(other)
+        result = date <=> other.date
+        result = value <=> other.value if result == 0
+        result
+    end
+
+    private
+        def validate_input
+            raise ArgumentError, "Date is required" unless @date.is_a?(Date)
+            raise ArgumentError, "Money or Numeric value is required" unless @value.is_a?(Money) || @value.is_a?(Numeric)
+        end
+end