Sigel updates

* Divide time span for Sigel updates into smaller intervals (interval size can be specified)
* Pass arguments for update processing to main method of Enrich: (1) start of download (i.e. the date of the base dump creation) and (2) the interval size in days
* Use proxy url "http://gnd-proxy.lobid.org/oai/repository" instead of "http://services.d-nb.de/oai/repository" in order to start the transformation from server
* Put transformation of sample data into separate class (EnrichSample.java): This class can be used for demonstration hbz-externally and for Unit testing
* Pass file path of dbs data to the processDbs method of the class Dbs.Java; this is parallel to the processSigel method of the class Sigel.java and allows to change the file path within Enrich.java