Change MUQ CMake so that MUQ can be included without other projects using add_subdirectory

[Matthew Parno]

• Don't write to CMAKE_INSTALL_PREFIX at compile time, only install time. May not have permission on that directory.
• Generated FooConfig.cmake should probably be named for MUQ, i.e., MUQConfig.cmake, not the CMAKE_PROJECT_NAME, otherwise it'll be called DakotaConfig.cmake for the MUQ subdir.
• All generated files should be in CMAKE_CURRENT_BINARY_DIR or MUQ_BINARY_DIR, not CMAKE_BINARY_DIR (top-level), otherwise they could clash with Dakota's.

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[Matthew Parno]

This has been fixed.