Pushed a bit earlier to enable new analytics.

[Gameplay]
- Changed zombie major so they spawn from tombstones and actually climb out of the ground
- Nerfed heatwave fire sprites a bit, they move slower and attack a bit less often
- Increased the frequency of minor tollbooth events for low car flow
- Added Bigfoot

[Other]
- Added more analytics
- Hid cheats behind sv_cheats 1 command. When this command is used during a game it will also disable analytic uploads for that playthrough
- Added the frog, fire sprite, asteroid and tornado to the main menu screen. Made some minor animation tweaks to other things

[Known Issues]
- Some contract images and operations control images are missing (haven't added them in yet)

[Upcoming Changes]
Better tutorial flow
Car variety
More major events
Minor event images