Define custom data model; add alembic scripts; etc.

actually our "custom" data model is just rattail + rattail-corepos

rattail_demo/db/alembic/script.py.mako

@@ -0,0 +1,28 @@
+# -*- coding: utf-8; mode: python; -*-
+# -*- coding: utf-8 -*-
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+branch_labels = ${repr(branch_labels)}
+depends_on = ${repr(depends_on)}
+
+from alembic import op
+import sqlalchemy as sa
+import rattail.db.types
+${imports if imports else ""}
+
+
+def upgrade():
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade():
+    ${downgrades if downgrades else "pass"}