#1 No confirmation on quiting

[Kunshan Wang]

Reproduce:
1. Open, login.
2. Click the close button on the title bar.

What actually happened
1. The program actually quitted, silent, without warning.

What should happen
1. It should either let me confirm this (e.g. "Are you sure to quit OpenFetion?").
2. Or minimize the main window, instead.

This behavior actually scared me when the window disappeared and the program exited.