Improved algae system, information and death

- Algae only spawn in the taskbar so they don't clutter up the screen
- Algae have a higher reproduction rate so it's rarer for fish to prey on them all
- The price of selling algae has been lowered
- Fish can no longer starve to death, but not eating will stop them from growing
- The number of algae that can be spawned before they stop spawning has been increased from 5 to 10
- The game's operation is explained in more detail in the information panel
- When fish die of old age, they now give you 80% of their value, so that the user can stop worrying about their fish and place them in the background with greater confidence.