Fixes trailing spaces in y_serial
Adds context manager to Extractor for hierarchical queries
Removes old code from Parser
Improves data extraction in parser
Adds document type checking to parser

This is to avoid parsing ContractNotice xml which does not have the same information and attributes.
And as the ContractNotice just documents non-payed contracts among public administrations, they're irrelevant.
Adds some temporal validation to the parser running