- PVM: throw/handle exceptions inside constructor (file doesn't exist, file is not an image or image corrupted)
- PVM: add steps count field (how many steps were made)
- PVM: constructor takes filename string parameter
- provide an interface (abstract class) for all Qt-related operations (to make PVM independent on library used)
- docs: pol -> eng
- P[GUI]VM - virtual method: when the VM state changes, it should emit a signal to be caught by machine_widget (this will trigger GUI state update)