This updates `jest`, `ts-jest`, and `jest-environment-node` to the latest versions, in order to facilitate code transformations during `ts-jest`'s on-the-fly compilation that will become necessary once we move to ES6. (More detail on this to come in the PR which actually introduces said transformation, but TL;DR the way we use and extend `global` is fine if it's a `var` (which it is in ES5 Land) but less fine if it's a `const` (which it becomes under ES6), and we need to fix that for tests to run.)

It also updates `jsdom`. Together these updates meant that a larger number of packages needed to be downgraded in order for tests to run in node 8 and 10. This therefore also reworks the test script a bit to account for those changes. Finally, this removes the test environment from our main jest config, as its value has become the default in latest version of jest.

As part of the new build process, a fair amount of new rollup-related code is going to be added. To keep things from getting too unwieldy, this splits the existing code up into modules. It also makes two other small changes, one for consistency and one to differentiate the current rollup code (which is for building bundles) from the future rollup code (which will be for building npm packages):

- All plugins are now generated through factory functions (`makeXXXPlugin`).
- Both the `makeConfigVariants` function and the individual `rollup.config.js` files have been renamed to make it clear they're for creating bundles.

For now all of the resulting modules live in a `rollup` folder at the top level of the repo. In the long run, these would be good candidates to go into an `@sentry-internal/dev-utils` package.

Delete old transports as we've switched entirely to new v7 transports.