How IGB loads data from a DAS server.

This is the current procedure for loading data from DAS servers. Currently,
this only works on two DAS servers:

UCSC = http://genome.cse.ucsc.edu/cgi-bin/das/dsn
Ensembl = http://www.ensembl.org/das/dsn

Proposal for using the DAS registry to find data.

It is possible to use the DAS registry to find data on DAS servers,
the problem is that all DAS servers can be set up differently, they
all follow different rules, some don't follow all the rules,
and some are not maintained.