Add views similar to `django` like structure

[wangzitian0]

@vrongmeal Thank you for your work. I think gin was more likely to Flask, installed of Django. Django offer us a Generic editing views https://docs.djangoproject.com/zh-hans/2.1/ref/class-based-views/generic-editing/, and then we could inherit the view class in view.py. But we don't have that or golang interface. Why we need split them?

[vrongmeal]

This sample application seemed quite similar to that of any Django app. Even I think gin is more like Flask but architecture of this app seemed quite similar to that of Django or I should say the MVT architecture. Also, I felt there is no harm in keeping different things in separate files. :)