Move EUtils object into its own file

EUtils object has been moved from util package object to its own file. A more
complete subset of Entrez Utilities WSDL files has been put into resources/xsd
and resources/wsdl directories. It can handle now all eutils basic stuff and
efetch into the PubMed database.

With that, search and download of PubMed documents has been implemented inside
the EUtils object (and tested in EUtilsSpec). Currently, searching of PubMed
ids returns an ESearchResult object (from scalaxb & generated code), maybe it
would be cleaner to return a tuple (CounterOfResults, SeqOfFoundIDs). Download
of PubMeds requires a sequence of Pubmed document IDs, and downloads them as a
sequence of tuples (PubmedId, Title, Abstract), since no more data is required
at the moment from the EFetchResult object.