refactor: rework calendar day view

Unfortunately, this commit combines a few changes:

* the calendar day view now uses the /program endpoint
  like the week view and therefore no longer needs to generate
  slots that fill empty spots in the program
* the visual presentation has been reworked so that it is
  more in line with the changes to the week view
* the look has been changed to a continuous timelime
  giving users clear feedback on what has been broadcasted,
  what is being broadcasted and what will be broadcasted

refs #128