Add setting for weeks activities open in advance to group level

User story: It would be helpful to set the weeks activities open in advance on a group level and to have an option to disable this setting in places. When changing this setting on a group level, a confirmation dialog with a warning that all places will be overwritten should be shown. If the group setting that this can be changed on a place level were enabled, you could still overwrite the value set per place.

Context: In my group, many places need to be managed, and we have introduced a rule that all activities should open 2 weeks in advance to reduce the behavior of people blocking slots a long time in advance, often without really knowing whether they are available.