Add support for packages that aren't in Maven

[milesziemer]

This is related to #67 , but would be a more comprehensive fix. If your model uses some packages that aren't available in Maven, builds can be successful but the language server will not be able to resolve the dependencies and provide its features with any traits or shapes you use from those dependencies. One idea on how we might be able to do this is if these dependencies are jars somewhere locally, we could provide these paths to the language server directly.