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/models/import/account_mapping.rb

@@ -0,0 +1,45 @@
+class Import::AccountMapping < Import::Mapping
+  validates :mappable, presence: true, if: -> { key.blank? || !create_when_empty }
+
+  class << self
+    def mapping_values(import)
+      import.rows.map(&:account).uniq
+    end
+  end
+
+  def selectable_values
+    family_accounts = import.family.accounts.alphabetically.map { |account| [ account.name, account.id ] }
+
+    unless key.blank?
+      family_accounts.unshift [ "Add as new account", CREATE_NEW_KEY ]
+    end
+
+    family_accounts
+  end
+
+  def requires_selection?
+    true
+  end
+
+  def values_count
+    import.rows.where(account: key).count
+  end
+
+  def mappable_class
+    Account
+  end
+
+  def create_mappable!
+    return unless creatable?
+
+    account = import.family.accounts.create_or_find_by!(name: key) do |new_account|
+      new_account.balance = 0
+      new_account.import = import
+      new_account.currency = import.family.currency
+      new_account.accountable = Depository.new
+    end
+
+    self.mappable = account
+    save!
+  end
+end