ctrl-c / ctrl-v clipboard callbacks never called on OSX

[jvcleave]

ctrl-c / ctrl-v clipboard callbacks never called on OSX

[borg]

A few steps towards a solution. The is_super_down mod to imgui above and this does seem to work. It seems just returning &ofGetWindowPtr()->getClipboardString()[0] returns a variable that goes out of scope. Creating a static instance helps with that, but I'm not sure if it is being released somewhere else after. Another pair of eyes wouldn't hurt.
In general it seems because keyboard inputs are platform specific this is a bit unsupported in imgui.

	//--------------------------------------------------------------
	const char* BaseEngine::getClipboardString()
	{
        static string str = ofGetWindowPtr()->getClipboardString();
        if(str.size()){
            str = &ofGetWindowPtr()->getClipboardString()[0];
            return str.c_str();
       }
        return "";
	}
    

	//--------------------------------------------------------------
	void BaseEngine::setClipboardString(const char * text)
	{
        static string str = ofToString(text);
		ofGetWindowPtr()->setClipboardString(str.c_str());
	}
    

[rjx-ray]

Ctrl-C & Ctrl-V work OK on Win32 , but direct calls to getClipBoardString don't.

See #56