Add new search fields to the "Search NCBI Genbank" dialog

There are different tags that can be used during the search in NCBI Genbank. They are all enlisted here: http://www.ncbi.nlm.nih.gov/entrez/query/static/help/Summary_Matrices.html. A member of our vk public page asked about the possibility of search by exact sequence length: http://vk.com/uniprougene?w=wall-74359225_201. This search can be done by writing a string "<min_length>:<max_length>[Sequence length]" to a search field. However, it'd be handier if this tag was available in the combobox along with "Organism", "Gene" and other search parameters. Other Entrez tags are to be considered as well.