#274 Created a main method in PrintStatisticsReport

With this main method the statistic report can be generated without
starting Wunda.
 #247 created inner class DataSourceAccumulation

A accumulation of JRDataSource which is used by the statistics report to
provide each of its subreports with the correct JRDataSource. The needed
data for the creation of the JRDataSources is fetched via a ServerSearch
once, although this ServerSearch uses multiple queries.
 #274 added the other getter for the data sources
 #274 renamed server search

The server search was renamed and some comments to
BillingStatisticsReport were added.
Merge branch 'feature/274-charts-Geschäftsstatistik' into dev