Standardize usage of username and fullname / email throughout

[ianlivingstone]

We reference email, username, and full name throughout but we're not consistent about where they are used and when.

Let's come up with a simple guide line for when we use each one and how we refer to them. For instance, in the path we refer to identity, but this is a username or machine name. Other places, we use the full name and username.

If we could standardize, it'd be easier for a user to grok the system.