This adds an environment variable, HELM_NO_PLUGINS, that can disable
the plugin system from loading plugins. It provides a general way for
turning the plugin system off.

Closes #1624

docs(named_templates): fixed broken template

Adds "Workflow Umbrella Chart" article to related.md

docs(index): Move doc index into a separate file.

docs(related): add CI/CD docs

fix(helm): fix broken cache paths in repositories

This removes the full TOC from the README and puts it in an index. This
will help when we begin to autogenerate a website based on
documentation.

Closes #1564

A regression was committed during 2.2.0 that broke the repositories.yaml
file format, switching the cache path from relative to absolute. This
fixes the error.

Closes #1974

fix(style): add missing comments

feat(*): add support for test-failure hook

fix(kube): prevent recreating pods without a selector

resolves #1927

chore(docs/): document `helm test` feature

feat(helm): add conditions and tags

feat(helm): add local path support for deps in requirements.yaml

feat(helm): add cleanup flag to test command

nit: fix spelling of dependency

fix change requests

The following commands:
helm dep update
helm dep build
are now able to take a requirements.yaml with dependency charts' repo defined as:
file://../local/path or file:///root/path

closes: #1884

fix(helm): add warnings for missing chart dependencies

feat(*): add --namespace flag to 'helm list'

docs(related): Add link to croc-hunter video

When 'helm install', 'helm package', and 'helm upgrade' are run,
Helm will not issue any warnings if any dependencies listed in
a chart's requirements.yaml file are missing.  This change includes
warnings when a chart is found in requirements.yaml but isn't
in charts/.

Closes #1567