Draft: Add Jest and eslint

[scrblue]

Adds and configures Jest and eslint (over the unsupported tslint) and begins to add some initial unit testing.

Since eslint . --fix and the .editorconfig dropped cause a lot of mess in the diffs, here's a description of everything changed per commit:

• Add jest as a dependency -- Simply adds jest and ts-jest to the dev dependencies and adds a minimal jest.config.js
• Replace tslint with eslint did the following: add the .editorconfig, add eslint itself to the dev dependencies, copy the .eslintrc.js directly from the vircadia-web-sdk, and set up a minimal .eslintignore
• Temporarily remove prebuild stage removes linting from the build process temporarily. This is to be added again when the errors that cannot be --fixed have been solved.
• Update tslint inline comments to eslint inline comments did a simple find and replace from /* tslint:disable-next-line */ to // eslint-disable-next-line, however the .editorconfig muddied the diffs some.
• Run eslint with --fix argument does what it says on the tin, rewriting massive parts of the codebase
• Add util function to Db.ts for testing adds one function for directly setting the Datab global for use in unit tests, but again rewriting parts from the .editorconfig.

The final commits are relegated to their own files and can be reviewed easily by examining the diffs.

[Misterblue]

The name should change to "vircadia-metaverse", the author should be upgraded to "contributors", and the URL should be changed to "https://git.hub/vircadia/vircadia-metaverse" but I will include all those changes in a separate PR.

[Misterblue]

Lots of work getting the eslint rules passing. Great job.
Only one code suggestion.

[Misterblue]

Rather than "mockAccount", you could use "Accounts.createAccount(user, pw)". This returns an AccountEntity with all the fields and doesn't update the database.