Resolve "UI Improvements 2"

Closes #68 (closed)

⚠ Important changes:

• The default tickrate is now 10/s, an in-game day takes 60 ticks (before it was 30/s)
• Speed of visitors has been increased from 0.01 to 0.05
• Visitor arrival chance increased to 0.05 to deal with the lower tickrate

Implemented features / fixes:

• speed adjustment improvements #54 (closed)
• display statistics about how many people entered the park #47 (closed)
• remove smoothing when a person "teleports" #67 (closed) and #61 (closed)
• prevent invisible visitors from being selected #57 (closed)
• implement RollingAggregation<T> #70 (closed)