Account:: namespace simplifications and cleanup (#2110)

* Flatten Holding model

* Flatten balance model

* Entries domain renames

* Fix valuations reference

* Fix trades stream

* Fix brakeman warnings

* Fix tests

* Replace existing entryable type references in DB

app/models/holding/forward_calculator.rb

@@ -0,0 +1,21 @@
+class Holding::ForwardCalculator < Holding::BaseCalculator
+  private
+    def portfolio_cache
+      @portfolio_cache ||= Holding::PortfolioCache.new(account)
+    end
+
+    def calculate_holdings
+      current_portfolio = generate_starting_portfolio
+      next_portfolio = {}
+      holdings = []
+
+      account.start_date.upto(Date.current).each do |date|
+        trades = portfolio_cache.get_trades(date: date)
+        next_portfolio = transform_portfolio(current_portfolio, trades, direction: :forward)
+        holdings += build_holdings(next_portfolio, date)
+        current_portfolio = next_portfolio
+      end
+
+      holdings
+    end
+end