added article stats (needs serialization)

...-cmd/src/main/java/de/vipra/cmd/option/ImportCommand.java

...md/src/main/java/de/vipra/cmd/option/ImportException.java

vipra-cmd/src/main/resources/log4j2.xml

vipra-cmd/src/main/resources/log4j2dev.xml

...src/main/java/de/vipra/rest/resource/ArticleResource.java

...t/src/main/java/de/vipra/rest/service/ArticleService.java

vipra-util/src/main/java/de/vipra/util/model/Article.java

...-util/src/main/java/de/vipra/util/model/ArticleStats.java

...util/src/main/java/de/vipra/util/model/TermFrequency.java