Added command line option --state-file

 Added command line option --state-file to override default location of migrations/.migrate file.

This change is required to support node-migrate use in OpenShift. When Git repo is pushed to OpenShift, all files that are not under version control are deleted. For that reason the .migrate file has to be stored outside the repository - in $OPENSHIFT_DATA_DIR as suggested in http://stackoverflow.com/questions/25386232/incremental-db-upgrade-in-openshift. Parameter --state-file helps to implement just that.