Maximum lead /follow up time 15 minutes, don't take these times for
collision detection, fix duration display in templates table

Add quota of concurrent meetings per template, add informations while
selecting a template, check server availability, show the template of
the meeting in admin./edit table, permanent meeting can be disabled,
dates of non-permanent meeting are strictly observed and mandatory,
duration of meeting is exact (+ 1 minute)...

Allow the participants to change the assignment reviewers settings of an
assignment template