OO-1709: set current course version to 10, default recertification timelapse is 0, check if the value is an integer before casting

OO-1706: allow bulk download of individual tasks with only assignment or submission, rename the directory of the downloaded archive for individual tasks

OO-1691: add an option tp specify the port of the smtp host, add an additional optional for start tls to trust the host

OO-1695: for assignment and submission due date, remove the hour and minute if date only, minus one day ( meaning: user has the whole day to do the task ), for solution remove only hour and minute if date only ( meaning the solution appears at the date exactly )