Watchdog: remove VirtualWatchdog

We will provide documentation how to create your own VirtualWatchdog. It's simple,
create timeout and watchdog objects.

This class brought lot of discussion and questions. After our refactor we made this class
just a linked list of objects - something tickers can do as well (they already have linked list) and handling hw should be
done via Watchdog due to the limitations (timeout can be set only once per app!).

Author: 0xc0170