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/category_mapping.rb

@@ -0,0 +1,36 @@
+class Import::CategoryMapping < Import::Mapping
+  class << self
+    def mapping_values(import)
+      import.rows.map(&:category).uniq
+    end
+  end
+
+  def selectable_values
+    family_categories = import.family.categories.alphabetically.map { |category| [ category.name, category.id ] }
+
+    unless key.blank?
+      family_categories.unshift [ "Add as new category", CREATE_NEW_KEY ]
+    end
+
+    family_categories
+  end
+
+  def requires_selection?
+    false
+  end
+
+  def values_count
+    import.rows.where(category: key).count
+  end
+
+  def mappable_class
+    Category
+  end
+
+  def create_mappable!
+    return unless creatable?
+
+    self.mappable = import.family.categories.find_or_create_by!(name: key)
+    save!
+  end
+end