Add UI to the preferences that allows users to provide a default OpenShift server to connect to. In terms of widget we need a text-field for the server url and a checkbox that allows people to refer to the default server that is defined in the openshift configfurations (~/.openshift/express.conf and /etc/openshift/express.conf). If the checkbox is checked, the text-field is disabled, prefilled with the server that is present in the (rhc cli-tooling) openshift configuration. Once unchecked the user can enter a default server and override the openshift server that is configured in the configuration.