LUCENE-2308 Separately specify a field's type

by Nikola Tanković for Apache Software Foundation

Goal of this project is to refactor the Field Lucene API by introducing new FieldType class to separate Fields values from their properties and open way for easier Field extensions. This will result in more understandable instantiation of similar fields across documents. Field class, as part of core API, is very sensitive to shallow design or implementation which can cause drastic performance degradation due to its massive usage all over Lucene and Solr project, making this a challenging task.