v0.5.0

Using Java 11 now instead of Java 1.8.

Following updates were made:
Xtext 2.20 > 2.25
Lsp4j 0.8.1 > 0.10
Sprotty 0.8.0 > 0.9
Elk 0.6.0 > 0.7.0
Mwe2 2.11.1 > 2.12.1
Xerces 2.12.0 > 2.12.2