Add CMMN and DMN viewer

[pinussilvestrus]

Since we are able to simply render BPMN diagrams right now, it would be easily possible to extend the current functionality via dmn-js and cmmn-js.

[salaboy]

Before adding these.. can we add the properties panel?

[pinussilvestrus]

Jup, but that would depend on #2. I'll create an issue for that.

[salaboy]

Do you want me to label issues with priorities.. ??

[pinussilvestrus]

Would be nice 👍 You can do that via milestones if you like to, as I did it in #7

[bertisLongfellow]

Is development active, or deferred? I note the comments are 2019, the releases are 2020.

[budney]

I'm very interested in this as well. I have no experience writing VSCode extensions, or I'd try my hand at adding DMN support.