[REQ][php-slim4] Add dependency injection container

Created by: ybelenko

Is your feature request related to a problem? Please describe.

I've used current Slim4 server in my personal project and it's very handy to use predefined services/utilities within DI container, eg. database connection, gettext translation, send mail etc.

Describe the solution you'd like

Add PHP-DI/PHP-DI package to PHP Slim4 server. Maybe I'll add generator option to turn this feature off.