Disables index & sorting for urls' "html" field

[MrOrz]

Currently when we are writing HTML scrapped from the internet to urls index, we are getting these errors:

• https://stackoverflow.com/questions/24019868/utf8-encoding-is-longer-than-the-max-length-32766
• https://github.com/Stratio/cassandra-lucene-index/issues/13

SInce urls's html won't participate in searching, it's just a cached field that may be used when we improve summary extraction, we should turn off indexing and sorting (doc_values: false) for this field to avoid the errors above.