Added highlighting for current active content on the sidebar

[haddercone]

fixes #256

This PR adds UI enhancements for the courses Sidebar component to keep track of currently active content. It lets the user know where they are the course.

Video reference:

demo-1.webm

[hkirat]

pleaes fix merge conflicts, colors are very bad please clean them as well

[haddercone]

pleaes fix merge conflicts, colors are very bad please clean them as well

On it!

[haddercone]

@hkirat fixed merge conflicts with better colours. Please let me know your thoughts on this.

[haddercone]

Updated demo

demo-3.webm

[hkirat]

/bounty $15