Fixed few UI issues and added some features

Fixed:
- closing will not ask to save, and autosave is disabled
- removed Page stepper and unused code
- removed words completion feature
- added pragma statments
- moved opening database into function
- using alt+enter, multiple statements can be written — having the text insertion point at a query and pressing enter will execute that query
- result tableview header identifier used to be index of column title, now, its the column title itself (this will help when editing field from tableview is allowed to save changes in the database).
- private ivars starts with underscore