[deps] Xcore now depends on Xtext >=2.5.0

Change-Id: I463ba3cd1663c334bb9dd3e6066228aedb889759
[mvn] experimental xcore-runtime build (for xtext-maven-plugin)

Change-Id: I6e9a969c304d3044eaf51ce3977069742ff12817
Make GenModelSupport available from mvn plugin

Signed-off-by: Sebastian Zarnekow <Sebastian.Zarnekow@itemis.de>
Add mvn target folder to .gitignore

Signed-off-by: Sebastian Zarnekow <Sebastian.Zarnekow@itemis.de>