Soft reload playlist

[Noam-Bendelac]

On playlist update / on interval (also for other resource if necessary). On/before fetch start, keep the old value of the resource and set loading to true, then when fetch is done set loading to false and update the data value.

I thought I would have to refactor the Resource interface for this, but now I don't think I do; I just need to update the uses of resource instances.

[Noam-Bendelac]

While I'm at it, I will remove the updateResource function and just return a normal setter from useResource. All uses of the resource setter should be changed to use React setter function syntax and object spread like the current implementation of updateResource:

setResource(resource => ({
  ...resource,
  ...updates,
}))