added drawing activities

[bendhouseart]

This PR corresponds to PR #363 and adds two drawing activities to the demo protocol.

[yibeichan]

@djarecka hey, we are adding drawing to UI (see this ReproNim/reproschema-ui#363 ) and so have a new input which couldn't pass the validation. i guess we need to modify the validate function a bit to adjust for this change?

[djarecka]

@bendhouseart - I was checking our schema, and it seems like we already have a property that might work for you. Each Item in reproschema can have image property, and the value can be either uri or ImageObject.

Do you think you can reuse this property in reproschema-ui for the drawing input, instead of adding an additional one?

[bendhouseart]

@djarecka maybe? My first thoughts were to set backgroundImage via Vue and I just used the most straight forward method to do that. see -> https://github.com/ReproNim/reproschema-ui/blob/be784b66ae8d8a158853f70f857a74c5d0c18eec/src/components/CanvasInput.vue#L28

My reasoning was: align reproschema with Vue/CSS/html versus the other way round. However, if we're able to draw over an image element and separate that drawing it shouldn't be an issue. E.g. I'd like to keep things such that the background image remains distinct from "value": { "imageData": .....} in the jsonld for each response.

Would you be willing to merge this for now and then try to reuse the image property in place of backgroundImage for the next iteration? I've tested this in my own janky setup, but it'd be nice to show that it can work on the live version of the demoprotocol.