Arbitrary non-contiguous test numbers, rather than starting from 1

Exam serial numbers should start with 0, not 1 (just like the marks students get), at least optionally if not by default.

More generally, one could have a "first exam number". For example midterm-0 could start at 0 and midterm-1 at 1000 so that it is easy to identify them from the serial number.

In the last issue i submitted, gitlab rounded the assigned weight down to an integer, so I am trying an integral weight.