feat(helm): allow disabling plugins

chore(*): bump kubernetes v1.5.3

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

Add ToJson and FromJson template functions

fix(local-cluster): fix missing variable option

set $HOME in tiller container to /tmp

docs(chart_repository): fix bug in code example

docs(named_templates): fixed broken template

Adds "Workflow Umbrella Chart" article to related.md

`unbound variable` error occurs when docker-machine is not used.

Closes #1967

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