We needed to disable a few eslint-config-airbnb-base rules in order
to keep the number of line changes under control.  These should be
re-enabled asap.

Closes #51065

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This enables JavaScripts projects to have live previews straight in the
browser without requiring any local configuration. This uses the
CodeSandbox package `sandpack` to compile it all inside of an iframe.

This feature is off by default and can be toggled on in the admin
settings. Only projects with a `package.json` and a `main` key are
supported.

Updates happen in real-time with hot-reloading. We just watch for
changes to files and then send them to `sandpack` to allow it to reload
the iframe. The iframe includes a very simple navigation bar, the text
bar is `readonly` to stop users navigating away from the preview and
the back and forward buttons just pop/splice the navigation stack
which is tracked by a listener on `sandpack`

There is a button inside the iframe which allows the user to open the
projects inside of CodeSandbox. This button is only visible on
**public** projects. On private or internal projects this button
get hidden to protect private code being leaked into an external
public URL.

Closes #47268

update several webpack loaders and plugins

upgrade nodemon

upgrade karma

upgrade karma-webpack

update karma-jasmine to fix broken reporter timer

eslint has the possibility to ignore inline config `no-inline-config`, so we should use that

Upgrade to eslint `~4.12.1` which is the last known version where the camelcase bug does not persist