Allow filtering of article types

Good day!

I often found myself on my phone, using your site, going "mannnn, I want to see this demo, but I can't from this stupid phone." Then, when I'm back on the computer, I'm overwhelmed with all of the posts I haven't clicked and read yet, that I forget about the demos from a few days ago. Or, maybe I have a good hour of free time that I want to use watching/listening to the media section. But again, my simple mind gets distracted by clicking all of the articles.

So, this PR allows filtering of article types, hopefully helping others like me, who want to focus on one type of content.