New ITSA input (GAMIT station.info) and output (PBO off file)

A deliverable for the EPOS-GNSS project is the list of 3-component offsets associated with antenna changes.

The plan is to provide these using the PBO off format (example here: https://data.unavco.org/archive/gnss/products/offset/cwu.kalts_nam14.off)

To do this, and since the dates of discontinuities come from the GAMIT file station.info (ASCII file containing the various time segments for each station, with the equipement information), the ideal way to do this would be to have that station.info file as the station metadata input.