Tidy Up Code

[TRPB]

• Switch to PSR-4 from classmap
• Improve code quality score on scrutinizer by reducing complexity of most classes
• Implement $fields property in DataSource\Database

[solleer]

The fields property which is set on line 29 of DataSource\Database is never used

[solleer]

Also what is the criteria parameter for in the One relation because I can't find an explanation for it

[TRPB]

$fields is yet to be implemented. I want to make it so that instead of always using SELECT * it uses 'SELECT ' . implode(',' $fields) if it's set with the options of making some fields lazy loaded. For example, if you had a news website with articles where the text is LONGBLOB, in most cases you probably just want the title/author information, it's only on the article page that you'd want the entire article text. For this I'd want to be able to specify title, authorId in $fields and articleText in $lazyLoad

For $criteria in the One and Many relationships, it's so you can do something like this:

//Create a one-to-many relationship between authors and blogs, but only return blogs where deleted is set to 0
$authors->addRelation('blogs', new \Maphper\Relation\Many($blogs, 'id', 'authorId'), ['deleted' => 0]);

It allows you to specify additional rules for the relationship's WHERE clause

[tontof]

In order to be able to test only SQLite using --filter phpunit option, I was wondering if it could be possible to exact all tests in MySQL class test inside a trait file that is imported into both MySQL and SQLite files ?
That way, SqliteDatabaseTest won't extend anymore MySqlDatabaseTest.
I can do a PR if you think it's a good idea.