* (Metal/WindowListener) Fix duplicate symbol errors by
moving implementation of WindowListener to cocoa_common.m
* (Apple) Cleanup some conditionals
* (Cocoa) Cut down on OSX ifdefs in Cocoa-specific code
* (QB) Add rule for Metal - define HAVE_COCOA_METAL for now
when building for Metal, and HAVE_COCOA for non-Metal build
* Make necessary changes to Makefile.common and qb/config.libs.sh:
- Disable OpenGL for now for Metal build
- Take Metal conditional out of OpenGL block in Makefile.common
* (Metal) Header fixes for compiling without Xcode/Griffin
* (Mac) Some buildfixes for non-Xcode building
* (cocoa_common.h) Restructure to no longer use -DOSX
* (Apple) More buildfixes
* (Apple) Cleanups
