Replace hard-coded MUD School area update rules

[Synival]

(After #181)

We should replace the special logic used for refreshing the MUD School with specific area update parameters. In the JSON file, the rules should be:

"always_reset_age": 3,
"active_reset_age": 3

When loading areas, the MUD School should be detected, and the following values should be set:

if (some_check_for_mud_school (new_area)) {
    new_area->always_reset_age = 3;
    new_area->active_reset_age = 3;
}

(This is so we can keep the vanilla MUD School .are file while making the area update logic nice and consistent :D)