Ability to select and move existing strokes

[bew]

If you'd like to put out an incentive for implementing this feature, you can do so at https://issuehunt.io/r/bk138/gromit-mpx

Is your feature request related to a problem? Please describe.

I'm always frustrated when during a presentation I draw some strokes, then decide I'm moving windows around, and now the drawings are not at the correct place anymore.

Describe the solution you'd like

I'd like to be able to select part of the drawings, either with a rectangle selection or a lasso (free-form) selection, and have a way to move the selection over the new position of the window.

Describe alternatives you've considered

Erasing my drawing and starting over.

Additional context

Once the selection system is in place, other features could be implemented, like erase selection, rotate, scale... But I don't needs these for now.