Genre selection dropdown menu and adequate response in song retrieval

[eniteCZ]

This is a commit for lab 11:
I got rid of the old song retrieval function with nested async loops
Instead, I split it up:

• First, we get genres and let the user choose one.
• Then when the user selects we load a playlist from that genre and get about 40 of its songs.
• When the user hits the "Broaden my horizon" button we take 9 random songs from the 40 loaded before and show him the visualization.

What changed is just the stuff that happens before clicking the submit button. You still get the same array of 9 songs afterward for your visualization.