It's a great suggestion, and we will look into if we can implement that.
Meanwhile, you can use click, shift-click. Ie, click the first one in the group, hold down shift and click the last one in the group.
Note that this only works for marking, not unmarking. This is due to the design of the library we are using. We did not manage to implement the same thing for unmarking, which we should look at again though. Because I am unsure why.