Dynamics module: Third body dynamics

Created by: ChristopherRabotin

Spawned from #5 (closed) ; Requires #4 (closed)

• Get equations from Schaub & Junkins
• Validate with scripts using additional point masses of {Sun, Moon}, {Sun, Moon, Jupiter, Saturn}, and all defined planets but Mercury
• Provide timing numbers for reference
• Add validation results to the validation mark down page