28: expression helper moved to validation package

to avoid a dependency cycle detected by sonar

Change-Id: Ie57b6412f257983379017f811aa00494fecc490c
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/28
28: moved caching classes to runtime package

to avoid dependency cycle reported by sonarqube: cache classes use
runtime classes which use cache classes.

Change-Id: I8f7c84c6595635a1dcee69ca463748d134d53867
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/28
28: moved TraceUtils in the runtime package

To avoid a dependency cycle

Change-Id: If0c4fdba31945dc321485969ccb94510b85aefec
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/28
28: clean xtend-gen with org.apache.maven.plugins

Change-Id: I00b71f983aa6d6e8277b71416f3fb76aef6d23e3
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/28
sonar.issue.ignore.multicriteria

To ignore issue squid:S00100 for OutlineTreeProvider "Method names
should comply with a naming convention"

Change-Id: I2dc7a0272a40ba445f42f671520be413b39735da
34: Implement RuleApplicationTrace.clone correctly 

Change-Id: I0b2e905b212545889154e10d167970566e599ea5
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/34
34: log deep cloning exceptions

Change-Id: I4612f971f7bf917f5f0f9072ddfb8259a5ff7232
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/34
fixed constructor order in IssueCodes

sonar squid:S1213

Change-Id: Id80a0799b77e4e54f447d77b4afb412d8b467237
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/34
ignore sonar issue about tab chars 

Change-Id: I28815596160ef92c5173a4c5792da78caf2301da
34: removed duplicate code in xbase compiler

Closes #34

Change-Id: Idaf791c860ae00c966fa81ff5d59e2a673126d3d
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/34