[Slim] Add Basic authentication middleware

Created by: ybelenko

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.1.x, 4.0.x. Default: master.
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Description of the PR

Basic auth middleware verifies token from Authorization header. If token not verified it returns 401 http status code and quits script execution. User needs to implement verifyCredentials method in AuthBasic.php. By default this method always returns false to avoid security holes on production. My code swapped with tuupola/slim-basic-auth package. For a quick start, user needs to implement own authenticator in SlimRouter class:

$basicAuth = new HttpBasicAuthentication([
    "secure" => false,
    "authenticator" => function ($arguments) {
        $user = $arguments["user"];
        $password = $arguments["password"];
        // write your own code here, compare credentials with database etc.
        return false;
    }
]);

Test endpoint with Basic auth:

$ curl -X POST "http://petstore.swagger.io:80/v2/fake" \
    -H "accept: application/json" \
    -H "Content-Type: application/x-www-form-urlencoded" \
    -d "number=33&double=68.9&pattern_without_delimiter=FooBar&byte=fdfdfdf" -i

Output:

HTTP/1.1 401 Unauthorized
Date: Tue, 24 Jul 2018 08:54:42 GMT
Server: Apache/2.4.23 (Win64) PHP/7.2.7
X-Powered-By: PHP/7.2.7
WWW-Authenticate: Basic realm="Protected"
Content-Length: 0

cc @jebentier @dkarlovi @mandrean @jfastnacht @ackintosh