Add SQALE metadata to XML rule format (SQ5.3+)

[guwirth]

Extended rule file format supporting SQALE metadata in same file: add support to cxx plugin

• https://jira.sonarsource.com/browse/SONAR-6591
• https://github.com/SonarSource/sonarqube/blob/master/sonar-plugin-api/src/main/java/org/sonar/api/server/rule/RulesDefinitionXmlLoader.java

[Bertk]

Should the SQ-API of the C++ plug-in also be updated ? e.g. use <sonar.version>5.2</sonar.version>
I checked the new format (Bertk@a41d221) and I plan to rework the techn. debt settings but there are some more tasks to complete this effort:

• remove file com/sonar/sqale/cxx-model.xml
• remove <priority> from default-profile.xml
• use RulesDefinitionXmlLoader in class CxxRuleRepository
• remove SqaleXmlLoader from class CxxRuleRepository
  We should divide the effort ... (cppCheck, PC-lint, Vera++, RATS, VC-compiler, ...)

[guwirth]

@Bertk yes we should do this after this release. Goal with this release is to be still compatible with last LTS 4.5.