clawapps directory structure

Proposed directory structure for the clawapps:

Rather than having a series of nested directories as in past versions of Clawpack (e.g. apps/advection/2d/swirl/amr) the top level directory will contain directories with names like: advection_2d_swirl or tsunami_chile2010

The structure within these directories may vary with app. There might be no subdirectories or there might be subdirectories corresponding to different ways of solving the problem (e.g. PyClaw or AMRClaw), if these require substantially different sets of source files.