Implementation of a Hashmap added to images to allow for ComicVineImages
to be converted to Strings in the format denoated by Cassandra 1.2

http://www.datastax.com/documentation/cql/3.0/cql/cql_using/use_map_t.html
Simple unit test added for comicvineimages to test the new hashmap /
string builder feature.

String builder may best be utalised by extracting out the core
functionality and implementing in a general use utility for all pojo's.