- Replaced GTK/OS X (note different from Cocoa) clipboard code with SDL clipboard API.
- Removed requirement to link to GTK in order to compile with GTK support.
- GTK is no longer init'd if the GTK IWAD picker is not used.
- Our usage of GTK is such that the dynamic loader can work with both GTK2 and GTK3 depending on what's installed.
- Since we're accumulating a lot of library loaders I've built a generic interface as FModule which replaces TOptWin32Proc and the loaders in the OpenAL and Fluidsynth code.
The reason for this is that the macOS version uses a deprecated API and in order to correct this, the file needs to be compiled as Objective-C++ which requires a different extension.
