Added superclass support to dao_processor

[joshuatam]

Can support similar implementations:

import 'package:floor/floor.dart';

abstract class BaseDao<T> {
  
  @insert
  Future<int> insertModel(T model);

  @update
  Future<void> updateModel(T model);
}

@dao
abstract class ItemDao extends BaseDao<Item> {
  // Other Queries...
}