Rename `Server::ConfigData` to `ServerData`

This moves the `ConfigData` out of the `Server` file and renames
it `ServerData`. This is setup for passing the `ServerData` down
to the route, runner and having its data accessible in service
handlers. Ultimately, its needed throughout Sanfords stack and it
felt wrong to require the server everywhere it was needed. This
moves it to its own file but keeps it associated with the server
by renaming it with the `server` prefix.

@kellyredding - Ready for review.