Feature/group imports by namespace root

[RobGordijn]

The basic idea is to add a newline between the groups of imports with the setting

"phpNamespaceResolver.sortSeparateNamespaceGroups": true

Before

use Foo\Bar;
use App\User;
use Foo\Bar\Whop;

After sorting + sortSeparateNamespaceGroups enabled

use App\User;

use Foo\Bar;
use Foo\Bar\Whop;