Sidebar sections are DECLARED, not guessed from a position number

The section headings were derived from position ranges: 10-29 became Assets,
30-49 became Information. A number is for ORDER; it was never a statement about
meaning, and using it as one meant a plugin landed in whichever bucket its
number happened to fall in.

That is how USB Devices - an asset - came to sit under Information beside
GE-Enforce and Tech Tools, and 3D Parts with it. Nobody chose that. It also
meant two plugins picking the same number silently reordered each other:
Warranties and Guides both held 8, the tie broke on plugin load order, and
Guides rendered under Warranties rather than under Slides where it was asked to
go. Warranties moves to 9.

Each nav item now names its section and the renderer groups by what was
declared. An item with no section stays in the unlabelled group at the top,
which is the safe default: it appears, it is simply not filed.

Assets gains USB Devices and 3D Parts. GE-Enforce and Tech Tools move to a new
Fleet section - they are neither assets nor reference material, and calling them
Information was only ever an artefact of their position numbers.

Also: sorting used `position || 99`, and 0 is falsy in JavaScript, so Dashboard -
the only item that uses 0 - sorted to the end of its own group.

plugins/usb/plugin.py

@@ -70,6 +70,27 @@ class USBPlugin(BasePlugin):
             'docs': 'plugins/usb/README.md',
         }
 
+    def get_settings_cards(self) -> List[Dict]:
+        """Somewhere to actually turn the kiosk on.
+
+        The kiosk page tells an administrator to enable it in Settings under
+        USB. Without this card that place does not exist, and the instruction
+        is a dead end - the same trap the backups plugin shipped with, where
+        settings existed but only a shell could reach them.
+        """
+        return [
+            {
+                'group': 'USB Devices',
+                'to': '/settings/usb',
+                'icon': 'usb',
+                'title': 'USB Settings',
+                'description': 'Logged-out kiosk for taking and returning '
+                               'drives, and whether somebody may return a drive '
+                               'checked out to another person',
+                'position': 45,
+            },
+        ]
+
     def get_settings_defaults(self) -> List[Dict]:
         """Kiosk settings.
 
@@ -144,7 +165,8 @@ class USBPlugin(BasePlugin):
                 'name': 'USB Devices',
                 'icon': 'usb',
                 'route': '/usb',
-                'position': 45,
+                'position': 25,
+                'section': 'assets',
             },
         ]