Gives access to version information for each installed selector engine

For example

curl http://localhost:37265/version
{"version":"1.1.13.pre1","engines":{"shelley_compat":"1.1.13.pre1","calabash_uispec":"0.10.0.pre1"}}

See Shelly pull request

https://github.com/TestingWithFrank/Shelley/pull/7

which lets Shelly present version data.