Force BreakWindow focus on start by default.

(Based on commit by Ray Satiro)

- (BreakWindow::BreakWindow)
Enable force_focus_on_break_start by default.

- (W32ForceFocus::GetFunctions)
Use AttachInput() and MinimizeRestore() by default to steal the focus.

Prior to these changes Windows could stop Workrave's BreakWindow from
becoming the foreground window. This is by design in Windows. For more
information refer to the SetForegroundWindow() MSDN documentation.