Major: Symfony (3.)4 support and Twig namespaces

Due to some breaking changes in Twig, webpack-bundle 2.0 has been released to be made compatible with the new Twig version. To ensure a smooth upgrade, please ensure that you have the following in your project:

• PHP 7.1 or higher
• Symfony 3.3.0 or higher
• Twig 2.4.0 or higher

There are no configuration changes made in this version. If your project uses the package versions as mentioned above, you should not run into any issues when upgrading webpack-bundle to 2.0.

The following additional changes were made in this version:

• Use PHP 7 strict type declaration
• Use namespaced Twig classes, which are introduced in Twig 2.4 for future compatibility (e.g. \Twig\Environment instead of \Twig_Environment)
• Enforce code style using phpcs and enforcing the extra ruleset specified by Hostnet.
• The class CSSLoader was renamed to CssLoader because our code style rules enforce this.
• Generated file names for inline javascript/css source are now coming from TokenStream->getSourceContext()->getName() instead of TokenStream->getFilename(). The latter function was removed from Twig.
• Created FCQN services and added aliases to ensure BC.
• Made the bundle compatible with Symfony (3.)4