Added JSON along with comments and error handling

[mishra-aayush]

No description provided.

[shivam212]

I don't think this is what we want. What we want is

• A JSON file that works the same as the txt file, i.e stores the names of the channel.
• A helper function that writes the usernames of the channels the user would want to download the videos from.
• Another helper function that reads the usernames from the json file and sends it to the downloader function.

What you have you done is -

• A helper function which does both read/write together.
• Your invocation will each time run the user_input function and prompt the user. What we want is the user to have a seperate function to add usernames.
• The downloader function be invoked after reading all the channels off the json file, like we did with the txt previously.
  A simple menu when the program is run which asks the user to select from 1) add channel, 2) remove channel, 3) download videos would be great.(We can turn this menu to a CLI based menu with click in the future)
  Also don't use global anywhere, will hinder us in the future.