Results in WEKA should be sorted

[Amir Zeldes]

The WEKA exporter currently outputs results in a seemingly random order. They should ideally be ordered according to token index. Ordering the results by the ANNIS id of the first element (first column of the WEKA exporter) usually achieves this because SaltNPepper gives larger ids to elements later in a document (in terms of token index). Ideally, real token index based ordering should be used, but sorting according to ANNIS id (the first column of the export) would already be nicer than the current situation.