Broadcast: Common end times

issue ~~#195~~ aims to have a start now button which allows the user to much more quickly get the stream up and running. The quick fix which was done to implement this hard codes a default end time (5:30pm).

if the user selects start now, they should be presented with a couple of common end times which will end the stream on the same day at the given time, alternatively if they select other they can select any time as the end time as before.