Include sample filters using pedigree info when querying variants

[jtarraga]

To enhance variant queries, users should be able to use pedigree information or user-defined attributes.
It should be integrated in the query command line, e.g., using the parameter --sample-filter

Examples:
--sample-filter sex==MALE
--sample-filter age>60;sex==FEMALE

Both pedigree information and user-defined attributes are stored in the variant metadata file.