Add test coverage script (#929)

## Description:

Added a command "npm run test:coverage"
This could be added to the CI/CD to check if a pull request induced
regressions, and if it added propers tests.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

theodoreleon.aetarax

.gitignore

@@ -2,6 +2,7 @@ build/
 node_modules/
 out/
 static/
+coverage/
 TODO.txt
 resources/images/.DS_Store
 resources/.DS_Store