Refactoring add and edit timetable templates

also adding new way of adding lines
Minor fixes on timetables
Minor fix
Changing remove icon and adding events
removing timetable slug from templates and using timetable pk.
Adding first template to list timetables

if the class doesn't have one timetable linked yet and that there is
timetables available, it should list the timetables to the user.
I will change to use popover instead of listing the timetable schedule
directly, which will have a confirmation button either.