npmjs has fixed/lowered the cache expiry time now

Ref: https://npm.community/t/scoped-packages-have-latest-version-disappear-temporarily-soon-after-publish/633/7

fix(docker): resolve relative URLs from registry

The default prefix is library/. Using amd64/ as the prefix created weird
issues with pinning to digests that matched no images.

Closes #798

Adds support for GitHub-hosted presets, using the `github>` prefix. Supports single preset per repository only.

Example:

```json
{
  "extends": ["github>renovatebot/renovate"]
}
```

The above would extend the `renovate.json` inside this repository (probably not a good idea, but an example).

Closes #2102, Closes #2312

As mentioned in #2315 some docker registries don't support the digest header. This PR falls back to parsing the resulting manifest if the header is present.

Closes #2315 

Adds support for processing www-authenticate Header to obtain a token from the Docker servers. In particular, this enables Artifactory to work (without username/passwords for now). This is backwards-compatible to Docker Hub which issues this header with the current hard-coded URLs.

Removes custom Docker lookup code and instead integrates it with the generic lookup routine used by other package managers. Logic for digest support was added but is used by Docker-only for now.

Closes #2081, Closes #2276

Adds support for PIP_INDEX_URL from environmental variables for self
hosted version. This is used instead of any urls set in the config.

Renovate now ignores any upgrades that are marked as deprecated, unless the current version is itself also deprecated. The new config option `ignoreDeprecated` can be set to false to disable this if necessary.

Closes #1988

Adds config option repositoryUrls which can be used by pip to define an alternate host to pypi.

Closes #2181