11/nest topics

[pelonchasva]

These changes fixes item #11 , it implementes a reducer in order to compare the data and create a new set of objects that represent the grouped items.

[carolinaknoll]

Hello, @pelonchasva!

Thank you for your contribution! Also, sorry for replying this late.

I have been reviewing your code and testing it on the project, and while the code is okay, there seems to be a small problem where if you click a topic children element, it will think the father was clicked and render the father's list instead.

For an example, when you open "Front-end Development", and then select "CSS - Critical Path Tools", which is now a child of the CSS topic, it will open the parent page instead.

I have been testing and trying a few solutions on this between all of the end-of-year activities, and will merge your PR as soon as I find a solution for this that is good enough. 😄

Thank you once again!