use full_name instead of first and last name, test changes, schema improvements

db/migrate/20160606040848_create_payments.rb

@@ -1,16 +1,13 @@
 class CreatePayments < ActiveRecord::Migration
   def change
     create_table :payments do |t|
-      t.string :first_name
-      t.string :last_name
+      t.string :full_name, null: false
       t.string :last4
-      t.decimal :amount, precision: 12, scale: 3
+      t.integer :amount, null: false
       t.string :authorization_code
-      t.integer :status, default: 0
+      t.integer :status, default: 0, null: false
       t.integer :user_id, null: false
       t.integer :conference_id, null: false
-      t.datetime :created_at
-      t.datetime :updated_at
 
       t.timestamps null: false
     end