REopt.jl default outage start time(s) based on load

[hdunham]

Also see NREL/REopt_API#395
Need to decide whether to add this to Julia package and call that in API or just add to API
Since we are changing the webtool to use default outage start times to make the outage centered on the peak load of each of the four seasons, we should at least have an easy option for the REopt.jl/API users to do this. Maybe a new input, boolean or string for different options (like starting on peak versus centered on peak, or seasonal peak versus yearly peak), which would enable that. This would also enable the webtool to use the same function with an endpoint (job.views function, maybe calling a REopt.jl function in http.jl) to get the start time steps.