improve date and time selection workflow

as per comments from https://github.com/mdik in https://github.com/cryptoparty/cryptoparty.in/issues/13

I have been testing upgrading from http://www.eyecon.ro/bootstrap-datepicker/ to http://www.malot.fr/bootstrap-datetimepicker/ on another branch to get a better workflow for adding the time. Initial tests look good, some really light 'plumbing' to do to pass date/time validation. 
