Recoding cmake to use BLT

[rblake-llnl]

I've recoded things here to use BLT everywhere. This is a complete redesign of the Cmakefile and export system.

In particular, I've added flags so that we can link in AMS in a large multiphysics code. The flags I"m using are:

cmake \
-DBUILD_SHARED_LIBS=On \
-DBLT_SOURCE_DIR="$EXTERNAL_BLT_SOURCE_DIR" \
-DENABLE_CALIPER=Off \
-DENABLE_RMQ=Off \
-DENABLE_WORKFLOW=Off \
-DENABLE_TESTS=On \
-DAMS_ENABLE_DEBUG=On \
-DENABLE_CUDA=${WITH_CUDA} \
-DENABLE_MPI=On \
-DTorch_DIR="$AMS_TORCH_PATH" \
-DAMS_FMT_DIR="$AMS_FMT_DIR" \
-DHDF5_DIR="$AMS_HDF5_PATH" \
-DHDF5_USE_STATIC_LIBRARIES=On \
-DHDF5_WITH_INTEL_RUNTIME=... \
-DZLIB_DIR="$AMS_ZLIB_PATH" \
-Dnlohmann_json_DIR="$AMS_NLOHMANN_JSON_DIR" \
-Dtl-expected_DIR="$AMS_TL_EXPECTED_DIR" \
-DCMAKE_INSTALL_PREFIX=./install \
-DCMAKE_BUILD_TYPE=Debug \
-DCMAKE_C_COMPILER="${CC:-gcc}" \
-DCMAKE_CXX_COMPILER="${CXX:-g++}" \
../