Fixes #563, adds the ability to open a file directly in the IDE (with th...

...e correct editor), without adding it to the project (Windows).

Till now only working with Windows VS 2013, with VS 2010 I'm waiting for #522 to be merged in, Linux I'll do the next days, Mac someone else has to do the menu stuff (cause of no xCode / Mac in general).

So ToDo:
- [ ] VS 2010: merge menu fix (#522), and add this option,
- [ ] Add this option on Mac,
- [x] Test it on Linux / Platforms using USE_POLYCODEUI_FILE_DIALOGS and USE_POLYCODEUI_MENUBAR