Lamdera project support

This plugin supports Lamdera projects. A Lamdera project currently consists of:

• elm.json with a direct dependency to packages "lamdera/codecs" and "lamdera/core"
• Frontend.elm with a top-level definition named app defined by frontend
• Backend.elm with a top-level definition named app defined by backend

To get going, you can download Lamdera's compiler here: Download lamdera executable