Split script into admin and dev

TODO: remove duplication between db.py and db_dev.py (split into
multiple commits is intentional)

scripts/db_dev.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+#######
+# Extended set of database schema migration operaions.
+# For help, run `sh db_dev.sh -h`. 
+# For detailed help, see documentation at lib/galaxy/model/migrations/README.md.
+#######
+
+cd "$(dirname "$0")" || exit
+
+cd ..
+
+. ./scripts/common_startup_functions.sh
+
+setup_python
+
+python scripts/db_dev.py "$@"