Refactor code to set maxGC, maxCoverage (etc.) for the DataSet and not for the Sequence

[claczny]

Currently, the DataSetFactory normalizes the GC and coverage values of a Sequence with respect to the maximum in the DataSet. However, this should not be done in this way. The annotations that are provided for every sequence should not be modified per Sequence but rather only when needed, e.g., when preparing the plotting in ClusterPanel.