updated maven-compiler-plugin.version to 3.1
* partly moved to maven source 1.8 (java 8)
* using diamond operators heavily
* moved toStr, isEmpty, remove, toArray, distinct, contains and equals methods to SSStrU from SSEntityA and sub classes
* fixed SSStrU methods (removed unused ones as well)
* fixed addDistinct in SSEntityA sub classes
* provided a isXX method for instantiations of SSEntityA sub classes to avoid necessary checks in get methods
* further re-factored service callings via SSServCaller to uncouple services (-datatypes)