Suppress boost warnings in build

[oruebel]

Currently we see a lot of warnings during compile generated by the boost library. To make it easier to focus on warnings and errors generated by AqNWB itself, it would be nice to suppress warnings generated by Boost. I think the-isystem flag could work to tell the compiler to treat the BOOST directory as a system include directory, which should suppresses warnings from those headers. I.e., add something along the lines of COMPILE_OPTIONS "-isystem${Boost_INCLUDE_DIRS}" in the CMakeLists.txt