#243 Standalone GLSP implementation

[tortmayr]

Resolves #243:

• Implementation of the Theia-independent GLSPWebsocketDiagramServer
• Refactoring of GLSPTheiaDiagramServer to use a common codebase
• server-side implementation for the WebsocketGLSPServer + minor refactoring
• Add workflow-standalone example for testing
• Add tasks for running the standalone example in chrome

To start the WebsocketGLSPServer for the workflow example simply add "websocket" as launch argument (java -jar workflow-example-1.2.0-SNAPSHOT-glsp.jar websocket)

(Note: Due to know issues it's currently not possible to use JSON-RPC with LSP4J and websockets out of the box (see #243). So for now the WebsocketDiagramServer does not use the JSON-RPC protocol and instead communicates with the server by simply sending action messages to a specific endpoint.
This can be addressed in a follow-up PR once eclipse-lsp4j/lsp4j#314 is merged)

[tortmayr]

Counterpart commit for glsp-p2:
https://github.com/eclipsesource/glsp-p2/pull/3

[martin-fleck-at]

Tested both the new standalone application (and server) and the Theia application (and server) and could not find any problems with either. All tools seem to work as expected and servers are also reacting correctly.

Fantastic change, thank you Tobi!