Add clock to UI

- added QTimeEdit to control widget
- set up appearance of the clock
Add timer logic and update clock

- clock now counts down time
- user can change clock only in stopped state (s)
- when clock reaches 0 end condition is emitted
- Issue: precision of clock depends on QTimer
Several minor todo's resolved

- application icon set
- label with result centered and text changed
- clock changing can be disabled from settings.ini
- now user can't click on mice when simulation is paused