Update .gitignore, rename database.php to datasources.php

I don't speak much English.

## Problem
"/App/Config/database.default.php" was removed.
"/App/Config/datasources.default.php" was added.

## Solution
Rename "database.php" to "datasources.php".
I deleted "/App/Config" according to  the .gitignore file of the version 2.3. 

## Comment
Since I do not understand specification well, I have a possibility of being wrong.