Enable verbose query logging

See merge request gitlab-org/gitlab-ce!20976

This backports the https://github.com/rails/rails/pull/26815
and enables that for non-Rails5 and non-production environments.

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

Add support for Bitbucket Server imports

Closes #25393

See merge request gitlab-org/gitlab-ce!20164

Move xterm to a node dependency and remove it from vendor's folder

Closes #49741

See merge request gitlab-org/gitlab-ce!20588

Parse junit.xml.gz and calculate the difference between head and base

See merge request gitlab-org/gitlab-ce!20576

Use object.assign for default option

Improve blocked user tracking and fire some events only once

Closes #49784

See merge request gitlab-org/gitlab-ce!20959

Resolve "Unicorn development settings should match production as much as possible"

Closes #49756

See merge request gitlab-org/gitlab-ce!20919