Improvements to track building hotkeys

[ElectroLlama]

I'm trying out building track using the hotkeys and noticed a few small things that could be improved:

1. When placing chain slope up and then switching to flat for the top of the lift hill, the chains are removed. To follow the behavior of pressing flat, the chain should remain.
2. On the wooden coaster when placing a banked small turn, pressing slope up switches to the special straight-slope-to-banked-turn piece instead of the helix. It would make more sense if it switched to the helix first.
3. There is no hotkey option to select special tracks. A hotkey to cycle through the available ones would be nice
4. Otherwise, it's a cool and intuitive feature!