Version 0.6.0

We now allow admins to unblock handles of users who deleted their
accounts. The admin interface also received some bugfixes. On the API
side of things we support validation of SMTP certs and added an endpoint
that requires authentication for retrieving the configuration files.

Here's the list of changes:

Pull request #181 from azul/feature/allow_anonymous_config_access
 * Allow fetching configs if anonymous EIP access is allowed

Pull request #180 from azul/feature/messages-api
 * fix messages feature to match latest response format
 * add translation and fix tests
 * some cleanup of the messages api and cuke feature

Pull request #176 from azul/feature/api-authenticated-configs
 * cuke: drop jsonpath, use simple keys instead
 * make sure i18n key can be found (cascade)
 * clean up error assertions in tests
 * fix controller refactor and features
 * move fetch_user into module so it can be mixed in
 * send config files from ConfigsController
 * ApiController with API style auth
 * clean up and simplify error responses and test code
 * move unauthenticated api endpoints into separate feature
 * send static list of configs for now
 * use cucumber; initial ConfigsController
 * render valid json error if provider file not found
 * SessionsController#unauthenticated for 401s
 * separate login_required from access denied response
 * rename warden extension to patch the original

Pull request #179 from fbernitt/issue_5217_addendum
 * Moved check for allow_registration into filter.

Pull request #175 from azul/feature/view-for-valid-certs
 * allow querying for the expiry of a particular fingerprint
 * fix tests and simplify time calculations
 * Identity view cert_fingerprints_by_expiry
 * store expiry with cert fingerprints

Pull request #178 from fbernitt/issue_5217_allow_registration
 * Added allow_registration toggle.

Pull request #174 from azul/bugfix/admin-navigates-all-tickets
 * adopt ticket list test to new behaviour
 * only use user ticket(s) path for real users
 * stay on all tickets view when sorting (#5879)

Pull request #173 from azul/feature/unblock-handles
 * list identities based on search only
 * make link_to_navigation more generic and reuse it
 * Enable unblocking handles in identities tab
 * backport bootstraps 3.2s list-inline
 * move braintree initilializer into core
 * remove dummy app
 * create client certificates with generous not_before (fixes #5884)