CSV Imports Overhaul (Transactions, Trades, Accounts, and Mint import support) (#1209)

* Remove stale 1.0 import logic and model

* Fresh start

* Checkpoint before removing nav

* First working prototype

* Add trade, account, and mint import flows

* Basic working version with tests

* System tests for each import type

* Clean up mappings flow

* Clean up PR, refactor stale code, tests

* Add back row validations

* Row validations

* Fix import job test

* Fix import navigation

* Fix mint import configuration form

* Currency preset for new accounts

app/controllers/import/mappings_controller.rb

@@ -0,0 +1,43 @@
+class Import::MappingsController < ApplicationController
+  before_action :set_import
+
+  def update
+    mapping = @import.mappings.find(params[:id])
+
+    mapping.update! \
+      create_when_empty: create_when_empty,
+      mappable: mappable,
+      value: mapping_params[:value]
+
+    redirect_back_or_to import_confirm_path(@import)
+  end
+
+  private
+    def mapping_params
+      params.require(:import_mapping).permit(:type, :key, :mappable_id, :mappable_type, :value)
+    end
+
+    def set_import
+      @import = Current.family.imports.find(params[:import_id])
+    end
+
+    def mappable
+      return nil unless mappable_class.present?
+
+      @mappable ||= mappable_class.find_by(id: mapping_params[:mappable_id], family: Current.family)
+    end
+
+    def create_when_empty
+      return false unless mapping_class.present?
+
+      mapping_params[:mappable_id] == mapping_class::CREATE_NEW_KEY
+    end
+
+    def mappable_class
+      mapping_params[:mappable_type]&.constantize
+    end
+
+    def mapping_class
+      mapping_params[:type]&.constantize
+    end
+end