Some big changes in window handling

Fullscreen:
vid_customwidth is replaced with vid_width
vid_customheight is replaced with vid_height

Windowed:
vid_winwidth is added to specify window width
vid_winheight is added to specify window height

Window position and size are saved by default but can be toggled off
with:
vid_win_save_pos (default 1)
vid_win_save_size (default 1)