Support helm charts with dependencies and namespace sensitivity (issue #582)

[jessesuen]

• Run helm dep build before helm template to download a chart's dependencies. This allows charts with dependencies to be deployed (e.g. spinnaker, wordpress).
• Update the manifest for argocd-repo-server such that it runs without a service account token. This was done because helm was inferring the current namespace from this token, and the argocd namespace would be exposed in the chart's manifests. By removing the token, helm will use the namespace "default" in the manifests (when needed)
• Add a TCP readiness probe to argocd-repo-server (issue Add readiness probe to repo server #529)
• Some helm charts (e.g. spinnaker) are sensitive to the value of helm template --namespace NAMESPACE, because it incorporates the namespace into the manifests. To support these type of charts, a new namespace field was added to ManifestRequest so that these helm charts can be deployed with ArgoCD.
• Fix issue where helm hooks were being deployed as part of sync (issue Helm hooks are being deployed as resources #605)