Assign dimensions to the dectectors in the BASIS instrument file

[Jose Borreguero]

Current detectors lack proper dimensions. Thus the view instrument renders the detectors with boundaries not touching each other. Instead, there is a lot of "empty space" between contiguous detectors. This severely diminishes the usefulness of the view instrument, specially when selecting regions of interest.

[Stuart Campbell]

This ticket has been transferred to github issue ​12649