Combine interfaces for arrakis and nds
Uses a single interface to communicate with either nds or arrakis servers.
Data source is selected through the LIGO_DATA_URL environment variable.
CIT nds server:
export LIGO_DATA_URL=nds://ligo.caltech.edu:31200
Local mock arrakis server:
export LIGO_DATA_URL=http://localhost:31206
Also some other changes that improve performance, particularly with "in the past" arrakis data.