Add some MyOjectBox stub

You see, when you create new project you want to write all base default dependencies and ways to provide them (in case of dagger 2 - modules) but you can't do it with ObjectBox because if you have no entity there will be no MyObjectBox class.
Maybe it's possible to make some MyObjectBox stub that will persist from the beginning independent if there at least one entity class?

未指定文件、测试或入口点。首先定位 ObjectBox 的代码生成路径，并检查存在实体时 MyObjectBox 是如何生成的；确定项目中没有任何实体时的预期行为。完成的标准是：在没有实体类的情况下创建项目后即可获得可用的 MyObjectBox stub，并覆盖这一空项目场景。