Provide types for @happyguestmx/web-utilities

• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
• Add or edit tests to reflect the change.
• Follow the advice from the readme.
• Avoid common mistakes.
• Run npm test <package to test>.

Adding a new definition:

• The package does not already provide its own types, or cannot have its .d.ts files generated via --declaration
• If this is for an npm package, match the name. If not, do not conflict with the name of an npm package.
• Create it with dts-gen --dt, not by basing it on an existing project.
• Represents shape of module/library correctly
• tslint.json should contain { "extends": "@definitelytyped/dtslint/dt.json" }, and no additional rules.
• tsconfig.json should have noImplicitAny, noImplicitThis, strictNullChecks, and strictFunctionTypes set to true.