Update GTF parser to check for compulsory attributes

According to the spec[1], attribute values must start with "gene_id"
and "transcript_id"

[1] http://genome.ucsc.edu/FAQ/FAQformat.html#format4
Update GTF serializer to properly print compulsory attributes

Previously, attributes are printed as ".", resulting in a violation
of the GTF spec. This commit adds some checks to ensure that the compulsory
attribute keys are shown properly. Default values for these attributes
("") are still honored.
Update gtf_test1.sql to reflect changes to parser and serializer

Changes:
* the 'type' column is renamed to 'feature'
* gene_id and transcript_id order is reversed in all tables to reflect
  ordering in GTF file
Update GTF serializer to write all attribute key-value pairs