Fixed: Respect the libdeng2 "C API only" build option
This fixes a build failure.
Most of the plugins are currently compiled with DENG2_C_API_ONLY, which restricts the API of libdeng2 to just the C wrappers, i.e., no Qt-based functionality is exposed.
In this mode, we should not be including C++ headers and declaring classes.
Fixed: Respect the libdeng2 "C API only" build option
This fixes a build failure.
Most of the plugins are currently compiled with DENG2_C_API_ONLY, which
restricts the API of libdeng2 to just the C wrappers, i.e., no Qt-based
functionality is exposed.
In this mode, we should not be including C++ headers and declaring
classes.