Add a page about Plasma's features
We can use this app to surface some of Plasma's more useful features that other platform lack, helping people to learn about what makes Plasma unique.
As a by-product, the flow was tweaked a bit and a new controller function to run commands was added.
At the moment these pages are rather bare-bones, so I tried to keep their text length down. In the future we could add graphics, arrows pointing to the things on screen that you need to click on, video tutorials, Konqis, etc. But that will be a ton of work and I'd like to not consider their absence a blocker. I think this is useful enough in its current form as a starting point.
This might be a place for the "Plasma is made of widgets" explanation too.