Add "treat symbols as metadata" option to spec_helper
Ensure user and guest names don't exceed 50 chars
Set guest name with a "who" parameter

Including a "who=something" query param, you may now set the name of the
current guest user.

If the user had an active session already, we simply set the guest name
so long as they haven't already entered one. If the session has a guest
name already, we create a new session and set the name.

For example:

  http://beta.etflex.et-model.com/?who=Jeff
  http://beta.etflex.et-model.com/scenes/1?who=Britta

Closes #419.