make scene items use linked list rather than array (containers are a bad habit), add a few functions for getting scene item information, also use a mutex to prevent race conditions when using the linked list

- disable -Wshadow for c++ (less semi-bogus warnings for constructors)
- make gcc use c99 mode

make it use GetClientSize instead of GetMinSize for when resizing the panel (though at this point I don't think it's going to help anymore)

create a sizing callback for the preview panel specifically, apparently on macos the window size isn't guaranteed to be the size it's set to in the main window size handler

one of the problems of doing changes for Objective-C on windows is that you can't actually compile your code and test it before commiting, leading to foolish little errors like 'you forgot to put a semicolen at the end of that call'

not sure what was on my mind there but I totally got the variable names wrong in that last commit (for NSOpenGLContext update)

add wrapper for popup menus so you aren't forced to write a god forsaken function handler whenever you just want to do a basic popup menu