FeaturesViewEngine improvements

Previous versions of FeaturesViewEngine had issues with performance. It was caused because the library didn't cache view paths which it was not able to resolve. In the latest version, this is fixed.

I also added filtering for requests without a controller. So now it passes such requests further without trying to handle those.

Another addition is support for display modes. Thanks to my colleagues Klāvs and Kaspars. They made a pull request which fixes a missing feature.

They also added integration tests. Now it is much easier to refactor and improve the library without breaking anything.

I have created proper documentation for FeaturesViewEngine. You can view it on GitHub.