Create ESI GUI use case document

[tzumainn]

There seems to be considerable interest in the ESI GUI again; a use case document will help ensure everyone is on the same page. The cases covered should include:

• viewing leased nodes
• viewing available nodes and leasing ones that match certain parameters
• provisioning nodes
• opening up a secure console to a node
• viewing reports on node leases

[tzumainn]

I've started a use case document here: https://docs.google.com/document/d/1kGu--dV449m4paNm7ggakpLv6JXiFJstVy3BPbP2DV0/edit

Feel free to start filling stuff in; if you're not sure what it should look like, I can also do a few use cases first.

I was going to add examples of use cases I've seen recently, but I think this one will be different, as a description of the flow is important. I'd say start a use case, put in as much information as you think is relevant, and then we'll work together to figure out if there's a way to present the information that makes it easier for others to picture.