Add syntax highlighting

[Marwes]

Cloud 9 seems to have some support for importing textmate definitions https://cloud9-sdk.readme.io/docs/import-a-textmate-bundle so we might be able to use that + https://github.com/gluon-lang/gluon_language-server/blob/master/syntaxes/gluon.tmLanguage

[Marwes]

https://github.com/Microsoft/monaco-editor could be more likely to support a language server though it needs custom syntax highlighting to be written.

[brendanzab]

Might be easier to rewrite the client in Typescript, or even Reason if need be. Kind of frustrated with how hard Elm's JS interop is.