Simplify types carrying multi-IFO detector and noise-floor info

   - split MultiDetectorInfo type into MultiLALDetector and MultiNoiseFloor types
     (current usage indicates that it's better to separate these data structures)
   - use fixed-size MultiXXX arrays to simplify memory handling
   - adapted all affected lalsuite codes
   - adjusted octapps to this API change in issue refs #1090
   - refs #1084