Add setting to expose/hide "active in POS" customer flag

tailbone/templates/customers/configure.mako

@@ -0,0 +1,23 @@
+## -*- coding: utf-8; -*-
+<%inherit file="/configure.mako" />
+
+<%def name="form_content()">
+
+  <h3 class="block is-size-3">POS</h3>
+  <div class="block" style="padding-left: 2rem;">
+
+    <b-field>
+      <b-checkbox name="rattail.customers.active_in_pos"
+                  v-model="simpleSettings['rattail.customers.active_in_pos']"
+                  native-value="true"
+                  @input="settingsNeedSaved = true">
+        Expose/track the "Active in POS" flag for customers.
+      </b-checkbox>
+    </b-field>
+
+  </div>
+
+</%def>
+
+
+${parent.body()}