fix blog title not updating in nav menu
fix blog title not updating in nav menu

closes #5474
- sets the blogTitle property of config when the title setting is changed

acburdine/Ghost-Admin,TryGhost/Ghost-Admin,airycanon/Ghost-Admin,kevinansfield/Ghost-Admin,TryGhost/Ghost-Admin,acburdine/Ghost-Admin,dbalders/Ghost-Admin,JohnONolan/Ghost-Admin,kevinansfield/Ghost-Admin,dbalders/Ghost-Admin,JohnONolan/Ghost-Admin,airycanon/Ghost-Admin