adding evtol weight converge script

[mclarke2]

This is a neat script I used during my thesis. A few universities who reached out to me for eVTOL design also found it useful. It basically ensures that the weight of the vehicle simulated is the same as the guess weight used to compute the weights of individual components

[coveralls]

Coverage decreased (-0.0004%) to 90.222% when pulling 94edb442b04177d227ea4578a89ff60b907e9b94 on feature-eVTOL_weight_convergence into 8533b5ed2aefbbec67b4d1df6a39ad9c3d6bcf97 on develop.