Created migration classes for Admin, Users, Tasks, Subtasks. Added valid...

...aters for classes and set references

	new file:   app/models/admin.rb
	new file:   app/models/subtasks.rb
	new file:   app/models/tasks.rb
	modified:   app/models/user.rb
	modified:   db/migrate/20140825014844_create_users.rb
	new file:   db/migrate/20140924054743_create_admins.rb
	new file:   db/migrate/20140924060938_create_subtasks.rb
	new file:   db/migrate/20140924061518_create_tasks.rb
	modified:   db/schema.rb
	new file:   spec/models/admin_spec.rb
	new file:   spec/models/subtasks_spec.rb
	new file:   spec/models/tasks_spec.rb