[#4] Entity Framework is upgraded from 4.1 to 6.1

I needed full-featured Code First, so I changed it
[#4] Add LucyDb class to the project

It will manage the database.
[#4] Add Id to Post

This variable will be used as an id to every post.
[#4] Posts are saved to the DB

Added LucyDb to the Write method.

We should use "using" keyword to automatically call Dispose() which closes the DB.
[#4] Fetch a post from the DB

Added the LucyDb to HomeController.Read().
Merge branch 'basic-read-write' to fix #4