Interrupt button should pause the timer

[ccidral]

Clicking on the interrupt button should pause the current pomodoro instead of aborting it. Then the user should be able to choose to either resume or abort the pomodoro.

Make this behavior configurable. In the options dialog, give the user two options regarding this behavior, something like this:

    Interrupt button should:

       (X) Abort the pomodoro
       ( ) Pause the pomodoro

The default behavior must be Abort the pomodoro, according to what the technique suggests. Also, show a warning saying that pausing the pomodoro is not recommended.