port of lucene-solr/lucene/classification w/o tests

Port of /lucene/classification/src/java/org/apache/lucene/classification (from lucene_solr_4_8_0 branch).

All the classes were ported in a separate project and solution files were added. Once I get a hang of this, I can port the tests too, just want to make sure I am doing this right.

Is this missing the `: IComparable<ClassificationResult<T>>` interface?