Adjust datetimepicker

no the hour format is european, font awesome icons are used. the only thing that does not really work yet is the restriction of the day. the end date should be the same as the start date
Adapting the start_time/end_time params in #create

the format is now alright from the beginning, no need to change it. so i got rid of #make_time and #make_time_string
Fix specs for new time format in start_time/end_time