Share rig configuration files with Imagine

[Cody-G]

Ref code review discussion in #23

It would be great if both this package and Imagine could share the same set of rig configuration files. Currently this package has one julia file per rig in the rigs folder of the source tree. Imagine has a separate set of javascript files in its source tree. The files in imagine are missing most of the information contained in the rig files here. We can decide on a common format (JSON?) and have just one set of configuration files that both this package and Imagine can read from. This would simplify development by reducing duplication of information (and potential for disagreeing information). It would also simplify the process of adding a new rig when either we or another lab build one.