Rename Metrics to Monitors and move it second

"Metrics" promised numbers. The tab holds tracked services, tracked processes
and network interfaces - things being WATCHED and their current state, only
one of which is a measurement. Monitors is what the panels actually are, and
it matches the word the agent's own config already uses for them.

Moved to second, ahead of Software. What is being watched on this box is the
question asked right after "what is it", and well before its application
inventory - which is reference data somebody goes looking for deliberately.

Tab order is now Details, Monitors, Software, Activity.

Contract 0.29.0 keeps its number. It is unreleased, so the group vocabulary it
introduces is still being settled and nothing can yet depend on the old name.
Both the server and the client fall back to 'details' for a group they do not
recognise, so a site that deploys these halves out of step gets a misplaced
card rather than a missing one.

Scope: product

tests/test_core/test_pluginui.py

@@ -198,7 +198,7 @@ def test_a_group_nobody_defined_falls_back_rather_than_disappearing(
     monkeypatch.setattr(plugin, 'get_asset_panels', lambda: [{
         'id': 'typo', 'title': 'Typo', 'assettypes': ['*'],
         'endpoint': '/api/whatever', 'render': 'keyvalue', 'position': 1,
-        'group': 'metrcis',
+        'group': 'montiors',
     }])
     assetid = _make_asset(db)
 
@@ -210,18 +210,18 @@ def test_a_group_nobody_defined_falls_back_rather_than_disappearing(
 
 def test_group_matching_is_not_case_or_space_sensitive(app, client, db,
                                                        auth_headers, monkeypatch):
-    """'Metrics ' is obviously meant to be metrics; do not send it to details."""
+    """'Monitors ' is obviously meant to be monitors; do not send it to details."""
     pm = app.extensions['plugin_manager']
     monkeypatch.setattr(pm.registry, 'is_enabled', lambda name: True)
     plugin = next(iter(pm.get_all_plugins().values()))
     monkeypatch.setattr(plugin, 'get_asset_panels', lambda: [{
         'id': 'shouty', 'title': 'Shouty', 'assettypes': ['*'],
         'endpoint': '/api/whatever', 'render': 'keyvalue', 'position': 1,
-        'group': '  Metrics ',
+        'group': '  Monitors ',
     }])
     assetid = _make_asset(db)
 
     panels = _data(client, '/api/pluginui/asset-panels?assetid=%d' % assetid,
                    auth_headers)
     panel = next(p for p in panels if p['id'] == 'shouty')
-    assert panel['group'] == 'metrics'
+    assert panel['group'] == 'monitors'