Fix mapping boolean values to string

As reported in #182 boolean values are mapped into string values due to wrong mapping being created for them and changes in autocasting mechanism started cast those values to the type of mapping. Changes here are changing mapping created to the right type. This MR requires reindexing with the force clean or other kind manipulation on the index as field types are being changed. Changes are on the schema parser level so if there are other methods of adding field to index schema they should be also checked if they use boolean instead of bool as boolean is valid storage type. Reindexing is important especially for indexes which are using copy_to mechanics or similar (like those where bag of words are enabled) as they don't allow invalid types to be added to string indices.