Improve ELK Layouting feature

[tortmayr]

Goal

The goal of this epic is to ensure that the current support we have for server-side layouting with ELK works expected in a generic fashion applicable to all source model and server flavors.
The main focus is to ensure hat the following core concepts work as expected

• Transformation of the graphical model to its ELK-graph counter part
• Layouting of the elk graph with the configured algorithm. This includes fine-grained configuration to e.g. not include certain element (types) in the layouting,
• Application of the resulting layout/graph to the source mode

Secondly, the elk versions currently in use are rather outdated and should be updated to the latest versions. This gives additional benefits like new or improved layout algorithms to choose from

In addition, related bugs and issues that are already tracked should be fixed as part of this epic as well.

Steps

Issues

• LayoutEngine/ELK layouting does no work well with custom source models #1173 [node/java]
• Update elkjs #1313 [node/java]
• Elk Layouting does not work in Theia when packaged as a VS Code Extension #1238 [Theia/VS Code]
• [elk] Element filter not applied to child nodes #1314 [Node/ Java?]
• Java server m2 build fails when using ELK 0.9.0 #1213 [java]
• Introduce unit tests for elk layout engine #1315 [node/java]

Java