Add start-end dates on listings page on council dashboard#245

It would help manage listings associated with a Council if each of the items in the list included the current start-end dates. If there are multiple blocks, this could be the earliest start and the latest end date. This information would allow us to ask Providers to delete old listings that they no longer intend to use (with new dates) or to ensure that all listings with dates outside the current booking window are unpublished and private