addon_config.mk to get rid of define OPENFRAMEWORKS

Manually toggling `#define OPENFRAMEWORKS 1` is awkward so I added `addon_config.mk` which passes `-DOF_OFXGVF` flag to projectGenerator. Thus, `#define` is no more required as far as projectGenerator is used. I only tried Xcode but VS and Linux Codeblocks should work as well.

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Btw, while compiling pd library to make sure there is no effect on it, `OPT_CFLAGS = -ftree-vectorize -ftree-vectorizer-verbose=2 -fast` is not recognized by the compiler (Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)):
```
g++ -I"/Applications/Pd-extended.app/Contents/Resources/include/pd" -I"../src" -DPD -DVERSION='"0.0"' -arch i386 -arch x86_64 -mmacosx-version-min=10.5 -fPIC -I/sw/include -g -ftree-vectorize -ftree-vectorizer-verbose=2 -fast -o "gvf.o" -c "gvf.cpp"
clang: error: unknown argument: '-ftree-vectorizer-verbose=2' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
make: *** [gvf.o] Error 1
```