Prevent data loss on timers - be resilient to browser crash and accidental tab close

Currently on Timer time sheet forms of you can loose already entered data when your browser crashes or you accidentally navigate away, e.g.:

• The timer is running and you accidentally close the tab/window. When you re-open the tab (Ctrl+Shift+T) all entered form data is lost in Chrome and the timer's state is lost in Firefox (but in FF at least the other parameters like Comments are kept, still the most important data, the duration, is lost).
  • The timer is running and your browser crashed. The same thing happens as above.

Long story short: if you are using Timers you can very easily loose its state either because of your or your browser's fault. This issue seems to not affect e.g. invoice forms.