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/transaction.rb

@@ -0,0 +1,17 @@
+class Transaction < ApplicationRecord
+  include Entryable, Transferable, Provided
+
+  belongs_to :category, optional: true
+  belongs_to :merchant, optional: true
+
+  has_many :taggings, as: :taggable, dependent: :destroy
+  has_many :tags, through: :taggings
+
+  accepts_nested_attributes_for :taggings, allow_destroy: true
+
+  class << self
+    def search(params)
+      Search.new(params).build_query(all)
+    end
+  end
+end