Sorry for confusion / #2087

I changed the name of the function getSum() to getMinMaxTime().

Originally I liked to use the function getSum() to get the sum of all efforts (like you described at the previous comment), but I found another solution (see effort.inc.php; I hope it's okay like this?).

But I needed another function to get the minimum and the maximum date of all selected efforts. Therefore I changed the code of the function getSum(), but I forgot to rename it.

I hope it's okay for you now?!

(Function getMinMaxTime() is related to the topic Show effort description.)