Refactor logic for reading and writing application and session settings:

* Introduce TAppSettings, created in dpr file
* Implement read and write methods, and replace callers of GetRegValue and MainReg.WriteInt/... with these
* Optimize read and write methods for avoiding redundant accesses to registry
* Auto-remove stored default settings from registry to avoid registry spam
* Replace synced MainForm.pref* variables with TAppSettings.Read* calls
* Move SetLocales call to dpr file
* Move MainForm.FDirname* variables to appropriate methods in helpers.pas
* Implement TQueryHistory.Create(SessionPath), reading its items within constructor

source/routine_editor.pas

@@ -122,7 +122,6 @@ end;
 destructor TfrmRoutineEditor.Destroy;
 begin
   // Store GUI setup
-  OpenRegistry;
   Mainform.SaveListSetup(listParameters);
   inherited;
 end;