Add the printedparts plugin: 3D-printed parts storefront and kiosk

Catalog with photos and append-only print-file revisions, a stock
ledger attributing every take/restock/adjust to a badge-resolved
employee, a touch kiosk (scan bin, scan badge, keypad quantity) with a
deliberately open decrement-only take endpoint, 1x0.5in CODE128 bin
labels, low-stock email alerts to selected users, roles, or addresses,
and stock/consumption/by-person reports with a cache-vs-ledger
reconcile. Ships disabled; enable per site. Contract 0.13.0 adds the
mailer and the User/Role models to the plugin surface.

plugins/printedparts/migrations/script.py.mako

@@ -0,0 +1,24 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+branch_labels = ${repr(branch_labels)}
+depends_on = ${repr(depends_on)}
+
+
+def upgrade():
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade():
+    ${downgrades if downgrades else "pass"}