Client should automatically start a language server

[tortmayr]

Currently we have to start the GLSP manually in an Eclipse instance. This is no issue during development and enables easy debugging however we should probably also provide a packed fat-jar of the glsp server which the client can start automatically in its backend process. (similar to the LSP startup in yangster https://github.com/theia-ide/yangster/blob/master/theia-yang-extension/src/backend/backend-extension.ts)

We would then also need two different startup configurations for the browser-app

• yarn start == Default startup where the client instantiates the language server in its backend

• yarn start:debug == Startup for development/debugging where the client simply receives the port on which the glsp server is running