Update to Symfony 4.1 #149 (#160)

* updated to Symfony 4.1 #149
* updated to phpunit 7 #149
* downgrade ocramius/proxy-manager for PHP 7.1 compatibility #149
* fixed symfony deprecations #149
* replaced AdvancedUserInterface with custom user checker
* code sniffer fixes

composer.json

@@ -9,6 +9,7 @@
         "avanzu/admin-theme-bundle": "dev-kevinpapst",
         "beberlei/DoctrineExtensions": "^1.0",
         "erusev/parsedown": "^1.6",
+        "ocramius/proxy-manager": "2.1.1",
         "sensio/framework-extra-bundle": "^5.1",
         "symfony/asset": "^4.0",
         "symfony/console": "^4.0",
@@ -36,7 +37,7 @@
         "dama/doctrine-test-bundle": "^5.0",
         "doctrine/doctrine-fixtures-bundle": "^3.0",
         "friendsofphp/php-cs-fixer": "^2.10",
-        "phpunit/phpunit": "^6.5",
+        "phpunit/phpunit": "^7.0",
         "squizlabs/php_codesniffer": "^3.2",
         "symfony/browser-kit": "^4.0",
         "symfony/css-selector": "^4.0",