merge contacts and test

[mkwoods927]

This PR adds the merge_contacts function to the VAN class and includes tests. #772

[shaunagm]

@mkwoods927 looks like the linter missed a file. Why does it keep doing that? :(

Here's the issue:

You should be able to make the changes locally, and then do the following to add, commit and push your changes:

git add .
git commit -m "fix linting"
git push origin add_mergecontacts

[mkwoods927]

Thanks @shaunagm ! This should be fixed now.

[shaunagm]

Thanks for the contribution, Melissa!