Port Viper IDE to the LSP frontend of ViperServer

[aterga]

As a result of a recent student project, we have a new (prototype) frontend to ViperServer, based on LSP, that complements the existing Http frontend. Using this frontend in the production version of Viper IDE would allow simplifying and improve the infrastructure since we wouldn't need a custom Http client implemented in Typescript on the VS Code side.

To make this happen, there are the following steps:

1. Review and merge the PR for Viper IDE (Client update to connect to ViperServer's language server viper-ide#113)
2. Learn how to efficiently debug the LSP frontend. Currently one needs to assemble a fat JAR and run the VS Code extension in order to start up the LSP server. There must be a way to attach to a version of the LSP server that was started by e.g. SBT; that would simplify the development cycle.
3. Test and debug thorougly, to make sure that the new solution is production-ready.