automated PR: update CoC and legalese

README: expand connector docs and assign each a level of support

Documentation: restructure connector docs to a single folder

Add Prometheus metrics

document limitations in the OpenID Connect connector

license: add bill of materials.

Clarify email scope description

Update slapd.sh

Correct "Verifier" method name in using-dex doc

Change provider.NewVerifier to provider.Verifier per the godocs:
https://godoc.org/github.com/coreos/go-oidc#Provider.Verifier

Bugfix: Set a proper status code before sending an error status page

*: fix proto build

Implement Microsoft (Azure AD) connector

Specify Java package for dex Protobuf API

Microsoft connector now provides support for 'groups' claim in case
'tenant' is configured in Dex config for the connector. It's possible to
deny user authentication if the user is not a member of at least one
configured groups.
Signed-off-by: Pavel Borzenkov <pavel.borzenkov@gmail.com>

connector/microsoft implements authorization strategy via Microsoft's
OAuth2 endpoint + Graph API. It allows to choose what kind of tenants
are allowed to authenticate in Dex via Microsoft:
  * common - both personal and business/school accounts
  * organizations - only business/school accounts
  * consumers - only personal accounts
  * <tenant uuid> - only account of specific tenant
Signed-off-by: Pavel Borzenkov <pavel.borzenkov@gmail.com>

show "back" link for password connectors

README.md: remove milestones link

This way, the user who has selected, say, "Log in with Email" can make up
their mind, and select a different connector instead.

However, if there's only one connector set up, none of this makes sense -- and
the link will thus not be displayed.
Signed-off-by: Stephan Renatus <srenatus@chef.io>

password connectors: make prompt configurable

This allows users of the LDAP connector to give users of Dex' login
prompt an idea of what they should enter for a username.

Before, irregardless of how the LDAP connector was set up, the prompt
was

    Username
    [_________________]

    Password
    [_________________]

Now, this is configurable, and can be used to say "MyCorp SSO Login" if
that's what it is.

If it's not configured, it will default to "Username".

For the passwordDB connector (local users), it is set to "Email
Address", since this is what it uses.
Signed-off-by: Stephan Renatus <srenatus@chef.io>

*: update maintainers

*: Go 1.7 no longer supported and updated build image to 1.9