Update base projects (model and UI)

- Consistently configure the following builders:
	org.fortiss.ide.dev_tools.warnings.RemoveWarningsBuilder
	org.fortiss.ide.dev_tools.warnings.GuidelinesChecker
	org.eclipse.m2e.core.maven2Builder
- Configure JDK 1.8 also in .classpath
- Bump plugin version to 2.9.0 in pom.xml
- "model" plugin
	- Move "compose" package here
	- GenModel: Do not generate array accessors (caused compilation errors in generated code for some models and option is apparently not used in AF3
	- Remove .DS_Store file
	
Refs 2512