Document chart best practices related to RBAC.

Fixes #3098.

This puts pointers to RBAC and TLS docs in the quickstart guide.

* support output-dir when running 'helm template'

* add --output-dir to documentation

* when writing to file, dont add additional document

* trigger another ci build. make test-unit works for me

* dont write blank files

* return err instead of panic

* docs(helm): Document how to update a release idempotently

To use the same command when installing and upgrading a release, using helm upgrade with '--install' works.

Closes #3134

* Upgrade instead of update

* fix(helm): add TLS params back

During a recent refactor, several TLS flags stopped being processed for
a few of the commands. This fixes those commands, and documents how to
set up TLS.

* fix(tiller): add stricter certificate verification

The older version of Tiller allowed a weaker set of certificate checks
than we intended. This version requires a client certificate, and then
requires that that certificate be signed by a known CA. This works
around the situation where a user could provide a self-signed
certificate.

Add helm-github plugin to list in documentation

Setting the value of `imagePullPolicy` should be aligned to what `helm create` does

Add helm-gcs plugin

feat(helm): Add a flag --dep-up that helm install will automatically execute helm dep up when charts are in requirements.yaml but not in charts

If checkdependencies returns an error, we can start download the
charts which are not in charts.

Closes #2879

Each maintainer can have an optional URL. There are seceral use
cases for providing a URL instead of an email address:
- The case where a maintainer wants to hide their email address
  behind a webform for personal security
- When the maintainer is an organization and feedback should
  go to an issue queue

This change:
- Adds the proto field for url
- Updates the generated files for the chart proto
- Includes linting for the url
- Updates the docs to include the url

Closes #3056

as requested

There must be at least one subchart or template file, therefore the `charts` and `templates` directories are not strictly optional.

Tested:
- Installing/deleting Chart
- Chart upgrade and Chart rollback

Add explanation of persistence behavior of `--set`

Fix a typo: `coffess`.

Adds documentation for running `tiller` with the new secrets backend
added in #2721

Document how to add an image pull secret in Helm

Provide an example of how to take an image registry, user name, and password and prepare a Secret that can be used by a pod to pull a protected container image.

This feature enables users to specify more control over where Tiller pod
lands by allowing "node-selectors" to be specified. Alternatively, the
"--output" flag will skip install and dump Tiller's raw Deployment manifest to stdout so user may alter it as they see fit (probably with a JSON manipulation tool like jq).

Closes #2299

>0.0.0-a does not match pre-releases on 0.0.0 that start with a
capital letter or number. This has to do with the ordering of
code points. Numbers and capital letters come before lowercase
letters.

>0.0.0-0 should match all valid pre-releases on 0.0.0. According
to the spec, "Numeric identifiers MUST NOT include leading zeroes."
A 0 is also the lowest code point for all the allowed characters
in a pre-release

* helm create all defined template names should be namespaced https://docs.helm.sh/chart_best_practices/#names-of-defined-templates

* Update Doc

* Update example