Add QD score offset to archives

[btjanaka]

Description

There are many archives which have negative objective values, thus making it useful to have a QD score which normalizes the objective values before summing them. This PR addresses that.

This feature will also be useful in the lunar lander tutorial, where we have negative objective values.

Credit to @SumeetBatra for suggesting this feature.

TODO

Questions

Status

• [x] I have read the guidelines in CONTRIBUTING.md
• [x] I have formatted my code using yapf
• [x] I have tested my code by running pytest
• [x] I have linted my code with pylint
• [x] I have added a one-line description of my change to the changelog in HISTORY.md
• [x] This PR is ready to go