Export explicit template instantiations on Windows.

Fixes an issue on Windows where tasks and adaptors could not be serialized or deserialized because each DLL linking to SMTK will create a unique template instantiation for Configurator<Task> and Configurator<Adaptor> which causes issues for any container that looks up by type id. Exporting explicit instantiations causes every DLL to share instantiations provided by the SMTK core library.