ClientRegistration Support baseUrl in template

[rwinch]

Summary

Instead of needing to type {scheme}://{serverName}:{serverPort}{contextPath} we should also support {baseUrl} (or some similar variable name) that composes all of those values. This should be in addition to the existing variables.

[rwinch]

Just setting a Milestone. Can push if necessary

[jgrandja]

I'll set the new uri variable name to be {baseRedirectUrl}

[jgrandja]

We may want to re-consider renaming from baseRedirectUrl to baseUrl