implement clipboard on OSX, fix hex and rob sliders on picker

src/app_events.cpp

@@ -19,6 +19,8 @@ std::string App::clipboard_get_text()
     return win32_clipboard_get_text();
 #elif __IOS__
     return [ios_view clipboard_get_string];
+#elif __OSX__
+    return [osx_view clipboard_get_string];
 #endif
 }
 
@@ -28,6 +30,8 @@ bool App::clipboard_set_text(const std::string& s)
     return win32_clipboard_set_text(s);
 #elif __IOS__
     return [ios_view clipboard_set_string:s];
+#elif __OSX__
+    return [osx_view clipboard_set_string:s];
 #endif
 }