Refactor|libdoom64: Switched wi_stuff.c to C++
Plugins: Added libdoomsday to dependencies

Todo: Address symbol conflicts (e.g., Uri vs de::Uri), cleanup...
Refactor|libcommon: Resolved conflicting symbols following libdoomsday dependency addition

Also fixed a couple of minor memory leaks; missing Uri_Delete()s

All plugins now build without error (on MSVC at least).