GRN2-253: Added the ability to share rooms across multiple users (#912)

* Added ability to share rooms with other users

* Fixed testcases

db/migrate/20191128212935_create_shared_accesses.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class CreateSharedAccesses < ActiveRecord::Migration[5.2]
+  def change
+    create_table :shared_accesses do |t|
+      t.belongs_to :room, foreign_key: true
+      t.references :user, foreign_key: true
+
+      t.timestamps
+    end
+  end
+end