Basic ASDC detector design implemented.

Very basic implementation using DetectorFactory so that detector parameters can be easily modified for testing. Similar to Watchman design but PMTs are triangle packed to access higher coverage fractions.

Basic use:
    /rat/db/set DETECTOR experiment "ASDC"
    /rat/db/set DETECTOR detector_factory "ASDC"

Detector parameters that can be changed are specified in the ASDC_PARAMS table in the ASDC/ASDC.geo file. E.g. to change the height of the detector to 50m:
    /rat/db/set ASDC_PARAMS det_height 50000.0 

No default PMTINFO included - this is generated on the fly in the factory.
I'd prefer to see this in a separate file named `ASDC_PARAMS.ratdb` -- makes it easier to find stuff when filenames and table names match.