Sandbox Mode, Cancer and more

Update! Summer is nice, I've had more time to work on the game lately. :)

-Sandbox Mode added

-Parasite boss re-added, now with giant health bar at top of screen

-Eosinophil re-added (fights parasite)

-Cancer Added (Credit to Aeratril Studio for beautiful cancer cell art)

-Ability to pause and fast forward levels added

Future work:

-Balance level speed (tends to be too fast for new players)

-Add  shop (Can buy antibiotics, tamiflu, vaccines)