Add super basic group model/command

PluralKit.Core/Models/Patch/GroupPatch.cs

@@ -0,0 +1,13 @@
+#nullable enable
+namespace PluralKit.Core
+{
+    public class GroupPatch: PatchObject
+    {
+        public Partial<string> Name { get; set; }
+        public Partial<string?> Description { get; set; }
+
+        public override UpdateQueryBuilder Apply(UpdateQueryBuilder b) => b
+            .With("name", Name)
+            .With("description", Description);
+    }
+}

PluralKit.Core/Models/Patch/ModelPatchExt.cs

@@ -60,5 +60,10 @@ namespace PluralKit.Core
                 .Build();
             return conn.ExecuteAsync(query, pms);
         }
+        
+        public static Task<PKGroup> CreateGroup(this IPKConnection conn, SystemId system, string name) =>
+            conn.QueryFirstAsync<PKGroup>(
+                "insert into groups (hid, system, name) values (find_free_group_hid(), @System, @Name) returning *",
+                new {System = system, Name = name});
     }
 }