get.Ts function and clean up

@lawinslow, not sure if you want a var-specific function in the helper.functions.R file, but that is where I put get.Ts. Didn't think grabbing the first index of wtr and assuming surface was safe. Could be 10m, could be out of order etc. 

Also, removing the "var not found" errors from the base functions, as R will error with a similar message and var names are pretty intuitive. And took out any sw from par swapping in base. It didn't make sense to me to have it in there.