return 409 for duplicate client ids

Clean up LDAP Connector

* Remove some unlikely to be used fields to help configurability.
  * Combined "serverHost" and "serverPort" into "host"
  * Remove "timeout" (just default to 30 seconds).
  * Remove "maxIdleConn" will add it back if users feel the need
    to control the number of cached connections.
  * Remove "trustedEmailProvider" (just always trust).
  * Remove "skipCertVerification" you can't make this connector
    ingore TLS errors.
* Fix configs that don't search before bind (previously broken).
* Add more examples to Documentation
* Refactor LDAPPool Acquire() and Put() into a Do() function which
  always does the flow correctly.
* Added more comments and renamed some functions.
* Moved methods on LDAPIdentityProvider to the LDAPConnector

return 409 status code on duplicate email errors

Fix docker-build script

*: update go-oidc to shorten length of key IDs

*: update mailgun-go to remove dependency on deleted simplehttp pkg

build with go 1.6 and actually push to quay

scope: don't validate empty scopes

If an empty scope is somehow passed along, it shouldn't be validated
when checking refresh token scope.

Allow specification of client_{id, secret} in admin api

You can specify your own client ID and secret!

Implement Public Clients

When "urn:ietf:wg:oauth:2.0:oob" is used as a redirect URI, redirect to
an internal dex page where the user is shown the code and instructed to
paste it into their app.

When calling manager.Authenticate, logs now show different error
messages.

* disallow ClientCreds for public clients
* clients can only redirect to localhost or OOB

Metadata is not enough these days - we're going to need access to the
Public field as well.

and update docs

  * Start Documentation

* validation of client moved into its own method and tested
* public clients have different validation - must have no redirect URIs
  and must have a clientName set

Revert "Use Github templates for issues/proposals"

The proposal templates was not intended to be show for every issue,
only for proposal. Revert that issue template and add more general
one in a follow up commit.

This reverts commit 09cb3857.

*: add --enable-automatic-registration flag to worker

For remote connectors, allow users to skip registration.

Remove old client_resource api

go 1.5.4 accepts just about anything as a URL, so instead just trigger
with blank URL