Change 0.0.0.0 to localhost

[gsganden]

I changed "0.0.0.0" to "localhost" in instructions and tests because it seems to work more broadly across different platforms.

One of the tests is failing at the moment because the file paths are out of sync. Merging #106 into master and then rebasing/merging for this branch should solve that problem.

Pull Request Checklist

• [x] Pull request includes a description of the change and the reason behind it.
• [x] Pull request uses keywords to close relevant issues.
• [x] Pull request includes unit tests for any new functionality.
• [x] README and docs have been updated.
• [x] ./.ci/local_checks.sh passes locally. (The app must be running. See README.md for instructions.)

Maintainer's responsibilities:

• [X] _version.py has been updated.
• [X] CHANGELOG.md has been updated.
• [X] Updated app container has been pushed, if relevant.