Fix invitation-based certificate exchange: auto-connect after invite.

Previously, invitations were working, but all that would happen was
certificates were exchanged.  No TLS connection was established.  This has
been fixed by adding some parameters to the 'storeExternalCert' message.

Jira issue: WP-852
Merge pull request #21 from jplyle/add-auto-connect-option

Fix invitation-based certificate exchange: auto-connect after invite.