Split Core modules into separate files

PluralKit.Core/Modules/DataStoreModule.cs

@@ -0,0 +1,19 @@
+using Autofac;
+using Autofac.Extensions.DependencyInjection;
+
+using Microsoft.Extensions.DependencyInjection;
+
+namespace PluralKit.Core
+{
+    public class DataStoreModule: Module
+    {
+        protected override void Load(ContainerBuilder builder)
+        {
+            builder.RegisterType<DbConnectionCountHolder>().SingleInstance();
+            builder.RegisterType<Database>().As<IDatabase>().SingleInstance();
+            builder.RegisterType<ModelRepository>().AsSelf().SingleInstance();
+            
+            builder.Populate(new ServiceCollection().AddMemoryCache());
+        }
+    }
+}