*: update go-oidc and use standard library's context package

examples/grpc-client: minor corrections in the dex client example.

Added produciton-users and integrations pages

server: fix expiry detection for verification keys

storage/kubernetes: enable HTTP/2 support

examples: adding a gRPC client example.

storage/kubernetes: fix conflict error detection in TRP creation

PR #815 fixed the Kubernetes storage implementation by correctly
returning storage.ErrAlreadyExists on POST conflicts. This caused a
regression in TPR creation (#822) when some, but not all, of the
resources already existed. E.g. for users upgrading from old
versions of dex.

Fixes #822

[storage.md] Fix the ThirdPartyResource syntax

This makes manually creating the `o-auth2-client.oidc.coreos.com` actually work.

storage/kubernetes: fix hash initialization bug

storage/kubernetes: fix kubernetes storage conformance test failures

[Makefile] Allow specifying VERSION as an env var

This makes specifying the VERSION when building native operating system packages require less hacks.

Refs: #811

simplified clone: using go get

storage: Surface "already exists" errors.

web/static/main.css: fix typo.

api: adding a gRPC call for revoking refresh tokens.

api: adding a gRPC call for listing refresh tokens.

storage: Add OfflineSession object to backend storage.

server: clean up test comments and code flow

Documentation: warn admins not to edit dex ThirdPartyResources manually

Fixes #706