New Service Description features

As discussed at the F2F, I'm going to add feature IRIs to indicate if a service supports empty graphs. I propose sd:EmptyGraphs.

Also, I had noted that we discussed a way to indicate if a CREATE statement is required/optional/noop. But based on the current state of Update, I'm not sure if this is actually needed. CREATE is marked at risk, and the insert statements indicate that they will create a missing graph. Does anyone think the service description needs to address this?

.greg