Refactor Livestream selection function to make more sense to me

[honboey]

At the moment, the function used to choose which Livestream to display is opaque to me. Refactor the code so it makes more sense.

I think the steps should be

• create empty dict
• loop through Livestreams and add Livestream and time till sunrise to dict
• sort dict by time till sunrise (low to high)
• get first livestream in sorted dict

[honboey]

This was done in #14.