Create tagging system (#792)

* Repro

* Fix

* Update signage

* Create tagging system

* Add tags to transaction imports

* Build tagging UI

* Cleanup

* More cleanup

app/models/transaction.rb

@@ -5,6 +5,9 @@ class Transaction < ApplicationRecord
   belongs_to :category, optional: true
   belongs_to :merchant, optional: true
 
+  has_many :taggings, as: :taggable, dependent: :destroy
+  has_many :tags, through: :taggings
+
   validates :name, :date, :amount, :account, presence: true
 
   monetize :amount