Squashed commit of the following:

commit 2bf28aae2d0a90c92732ec0ed85c8cc7e1c673d0
Author: Edvard Fonsell <edvard.fonsell@nitorcreations.com>
Date:   Fri Sep 26 10:02:44 2014 +0300

    add assert for workflow instance external id

commit d91034c7e3ed54b8d1275bcf2f10396809c285b8
Author: Edvard Fonsell <edvard.fonsell@nitorcreations.com>
Date:   Fri Sep 26 09:44:26 2014 +0300

    rename getWorkflowId to getWorkflowInstanceId and add getWorkflowInstanceExternalId to StateExecution

commit d68708c24c45b7e2f2b81eb760f8f93458eae51b
Author: Esa Puttonen <esa.puttonen@nitorcreations.com>
Date:   Wed Sep 24 10:08:04 2014 +0300

    Added getWorkflowId() to StateExecution