XWIKI-2155: Add license header check to the build

...ki/plugin/activitystream/api/ActivityStreamException.java

.../xwiki/plugin/applicationmanager/ApplicationPackager.java

...objects/classes/XObjectDocumentDoesNotExistException.java

...pplicationmanager/core/plugin/XWikiPluginMessageTool.java

...java/org/xwiki/rendering/macro/chart/ChartDataSource.java

...ventstream/src/main/java/org/xwiki/eventstream/Event.java

...eam/src/main/java/org/xwiki/eventstream/EventFactory.java

...tream/src/main/java/org/xwiki/eventstream/EventGroup.java

...ream/src/main/java/org/xwiki/eventstream/EventStream.java

...ain/java/org/xwiki/eventstream/internal/DefaultEvent.java

...a/org/xwiki/eventstream/internal/DefaultEventFactory.java

.../test/java/org/xwiki/eventstream/EventAndFactoryTest.java

...m/src/test/java/org/xwiki/eventstream/EventGroupTest.java

...java/org/xwiki/extension/AbstractExtensionDependency.java

...iki/extension/repository/AbstractExtensionRepository.java

.../main/java/org/xwiki/extension/repository/Searchable.java

...ension/repository/internal/DefaultInstalledExtension.java

...ki/extension/repository/internal/ExtensionSerializer.java

...xwiki/extension/repository/internal/ExtensionStorage.java

.../java/org/xwiki/extension/wrap/WrappingCoreExtension.java