Add vue-material-design-icons

[juliusknorr]

https://www.npmjs.com/package/vue-material-design-icons

Would allow us to make use of some nice icons, e.g. for adding lists/cards:

[jakobroehrl]

@juliushaertl @nextcloud/designers
Which deck icons I should change?

[juliusknorr]

Not sure yet if we need to change all in the first place, but if we find a matching replacement in the material icons it would make sense.