Create tagging system (#792)

* Repro

* Fix

* Update signage

* Create tagging system

* Add tags to transaction imports

* Build tagging UI

* Cleanup

* More cleanup

app/models/tag.rb

@@ -0,0 +1,25 @@
+class Tag < ApplicationRecord
+  belongs_to :family
+  has_many :taggings, dependent: :destroy
+  has_many :transactions, through: :taggings, source: :taggable, source_type: "Transaction"
+
+  validates :name, presence: true, uniqueness: { scope: :family }
+
+  scope :alphabetically, -> { order(:name) }
+
+  COLORS = %w[#e99537 #4da568 #6471eb #db5a54 #df4e92 #c44fe9 #eb5429 #61c9ea #805dee #6ad28a]
+
+  UNCATEGORIZED_COLOR = "#737373"
+
+  def replace_and_destroy!(replacement)
+    transaction do
+      raise ActiveRecord::RecordInvalid, "Replacement tag cannot be the same as the tag being destroyed" if replacement == self
+
+      if replacement
+        taggings.update_all tag_id: replacement.id
+      end
+
+      destroy!
+    end
+  end
+end