Affy -> Oligo schema and API changes.

Can now support oligonucleotide microarrays other than Affy.
The three affy_* tables are changed to oligo_* tables. New fields are:
  oligo_array.type (currently either AFFY or OLIGO)
  oligo_probe.length
  oligo_probe.description
The existing Affy objects become subclasses of new Oligo objects, but
the API is backwards compatible, so existing pipeline and Web code won't
need changing.