Highgui windows improvements

I've made 3 (small) improvements/fixes to the Windows Highgui project. They are fairly small and so I'm sending them in 1 pull request. If you like me to break them, I can. But they really are related and can go together. Here they are:

1. Using the correct, Windows TBBUTTONINFO, instead of the custom one. This fixes incorrect trackbar width due to incorrect struct "version."

2. Added support for changing the trackbar's max count after creation. Useful for dynamically changing the range.

3. Replaced the deprecated CreateToolbarEx, which avoids a warning (on newer VS) and a library dependency.

They can be merged into 2.4 as well. Can do upon request. Just let me know.