Add ability to add/remove subconditions for grouped conditions

[dehall]

Addresses #288 -- allows using more than 2 conditions in And/Or/At Least/At Most type conditions. It will also allow you to remove some but there's no reason to do that so it will add a warning if you have something that doesn't make sense. (For example "At least 4 of the following 3 conditions" doesn't make sense)