added tests to doxygen

test/decoupled/1p/benchmarkresult.hh

test/decoupled/1p/test_1p.cc

test/decoupled/1p/test_1p_problem.hh

test/decoupled/1p/test_diffusion.cc

test/decoupled/1p/test_diffusion_problem.hh

test/decoupled/1p/test_diffusion_spatialparams.hh

test/decoupled/2p/test_impes.cc

test/decoupled/2p/test_impes_problem.hh

test/decoupled/2p/test_impes_spatialparams.hh

test/decoupled/2p/test_transport.cc

test/decoupled/2p/test_transport_problem.hh

test/decoupled/2p/test_transport_spatialparams.hh

test/decoupled/2p2c/test_dec2p2c.cc

test/decoupled/2p2c/test_dec2p2c_spatialparams.hh

test/decoupled/2p2c/test_dec2p2cproblem.hh

test/decoupled/2p2c/test_multiphysics2p2c.cc

test/decoupled/2p2c/test_multiphysics2p2cproblem.hh