Namespace support in the compiler properties

While adding this I've seen FDBuild is broken... some of us have added code that reference classes inside PluginCore... I've added a reference to PluginCore, but this may bring some other problems.

The newly used classes could be added to FDBuild as some of the others currently present. If the way to go is referencing PluginCore I guess PluginCore.dll should be checked in as well, but all my tested compilations worked fine.