settings: fix conflict of <minimum> and <maximum> for CSettingList

While working on the settings system a bit I noticed that there is a conflict in CSettingList. It uses \<minimum\> and \<maximum\> to specify the minimum/maxmimum number of items in the list. But the same tags are read by the setting definition (e.g. CSettingInt for a setting of type "list[integer]") and used for the minimum/maximum value of the setting. Obviously this leads to unexpected conflicts.

I renamed the \<minimum\> and \<maximum\> tags of CSettingList to \<minimumitems\> and \<maximumitems\> to avoid this problem.