ENH: apply images_available_delay based on the end_date + the creation_date of image

[theroggy]

Now this is only used in calc_periodic_mosaic_task, should be centralized and generalized + behaviour should be changed like this:

• When image mosaics are calculated:
  • Now: the end_date is changed based on the images_available_delay
  • Change to: rather than changing the end_date, add the following to the check if an image exists in the image cache:
    • if the creation_date of the file <> of the current date, check if the creation_date - images_available_delay >= the end_date of the image. If this is not the case, delete it so it will be regenerated.
• When timeseries are calculated: the same logic must be applied, as the timeseries calculation is cached as well.