Several more database-y refactors

- DbConnectionFactory renamed to "Database", will now be the primary entry point for DB stuff
- Created IPKConnection interface mostly containing async extensions to IDbConnection, use this going forward
- Reworked the Connection/Command wrappers (that have performance/logging extensions)
- Probably more stuff that I forgot???

PluralKit.API/Controllers/SystemController.cs

@@ -40,10 +40,10 @@ namespace PluralKit.API
     public class SystemController : ControllerBase
     {
         private IDataStore _data;
-        private DbConnectionFactory _conn;
+        private Database _conn;
         private TokenAuthService _auth;
 
-        public SystemController(IDataStore data, DbConnectionFactory conn, TokenAuthService auth)
+        public SystemController(IDataStore data, Database conn, TokenAuthService auth)
         {
             _data = data;
             _conn = conn;