getNextDefaultId now properly assigned default IDs for derived stratum
classes.  Previously, the default ID of derived classes was calculated
by concatenating the default id of the parent class with the next
available id of for base classes, so lawn, inheriting from grass
(id=2) would get an id of 25 (assuming there were 4 base veg classes
(evergreen, grass, decid, and undeveloped).  Now the default id will
be 21.  The next stratum class that derives from grass would get id
22, etc.
Placeholders for eventual rain garden LU and lawn veg types
Updated to use $patch_rast for spatial extent of _stratum (instead of
$stratum_rast);  $stratum_rast is still used for the default_ID of the
_stratum
Added:
  - Rain garden LU class (6" detention store)
  - Deciduous class for mixed hardwood forests in the Baltimore Ecosystem Study
  - Lawn class to simulate eastern U.S. grasses with a maximum height of 10cm to simulate mowing