Dependency of Dan Zalkind's customized WISDEM and IEA15MW repositories

[yonghoonlee]

Currently the code is dependent to following external repositories in addition to WEIS:

1. Dan Zalkind's customized WISDEM with "linear_trim" branch at https://github.com/dzalkind/WISDEM/tree/linear_trim
2. Dan Zalkind's customized IEA-15-240-RWT with "hydro_lin" branch at https://github.com/dzalkind/IEA-15-240-RWT/tree/hydro_lin

I am hoping these changes could be merged into the main WEIS repository at https://github.com/WISDEM/WEIS

However, if this is not happening soon, I think we can think of merging these repositories into our FASTLin_DTQP_Driver repository, using git subtree feature.