Now noflo-ui uses a per-runtime-type hard-coded list of languages. However, in some cases this may depend on the installation. For example:
- NoFlo may or may not support CoffeeScript depending on whether the CoffeeScript compiler is present
- MsgFlo supports lots of languages, but only if their "runners" are installed
So, runtime:runtime message could return an array of supported languages.
Needed for noflo/noflo-ui#206