fix artefact.soString to include hidden inventory items. Add bike ambulance location
issue #187 implement bike ambulance mission
more on issue#187 modify "ask" to check for a keyword from "next" mission dialogue. Add a new mission condition attribute "conversationState"
issue #188 hide bike in rack. Improving hide actions.
fix object hide/show so that hidden objects are not unhidden at the wrong time and are made visible when collecting (removing from somewhere). Also fix a minor grammar tweak