Add the 'active' class to nav-items with an active child

This rebases !300 (closed). Placing the original merge request description

What does this MR do?

This MR adds the active class to nav items that have a child element with an active router link, through the use of the routerLinkActive selector.

This was done in order to later apply a CSS rule for the currently selected nav item to display in bold.

Related issues and links

This change is needed to address issue #33.

Other relevant links

This MR is related to universis!353 (closed), which is the one that actually adds the CSS rule for the active nav-item to be bold.

You can see screenshots of the end result over there.

Developer Checklist

• My code runs successfully locally

• I have submit screenshots of the code running locally

• My code works in all necessary screen sizes

• I have tested my code with different users to spot bugs

• My code has appropriate names for variables and comments in English

• My branch is up-to-date with the upstream master branch

• Coding is in progress, and I have marked the MR as WIP

• My MR follows the contribution guidelines

• I have added a comment with screenshots of the code running locally

Tech review Checklist

Have you verified that what is supposed to happen, actually does, and what is not supposed to happen, indeed does not?

• The MR accurately describes the changes and has a relevant title/description
• The MR does what it is supposed to according to its title, description and related issues/links
• I have successfully run the changes locally, and tried the new code

Overall review Checklist

• The MR references related issues/MRs
• The MR provides links to screens and screenshots
• The commits of the MR describe the changes, have proper wording, and follow the guidelines
• I have successfully run the changes locally, and tried the new code
• The MR is ready for merge (rebased, commit squashed if needed, etc)