feature: Adding a next button for watching the next video in the thread.

[akshathere]

Problem description
I'm always frustrated whenever I finish watching a video I always search for the next button so that I can jump over to video in the order. For eg :
If I am on 3.1 video, a button which on click takes us to 3.2 will be very helpful to make it more userfriendly.
Also

I am watching this video the side bar does not shows which week or video is selected. This feature will help tackle that problem as well

Solution
A solution can be linking the videos with each other (maybe use doubly linked list which can have prev and next as well . We can add a prev link as well (maybe not needed) but can add that as well.
All the video be sorted week wise and contains a prev button to go to prev video i.e if you are on video 8.2 prev will take you to 8.1
and A next link which takes us to 8.3 .

[SargunSinghSethi]

working on this

[shantanuSakpal]

@devsargam upon inspection, i found there was already a function getNextVideo. i wonder why it wasnt used?
also , if this pr is good, i can further add the getPrevVideo functionality as mentioned in issue