added interface to hot start capability

I think this is all that needs to be done. I tested it (although not thoroughly) and it seems to work. One thing to note however, is that I couldn't get the hot start working with the NSGA2 optimizer. Whenever I tried it, it would give me a segfault. This might be a bug in pyOpt. I emailed Dr. Perez one of the pyOpt developers to ask about it, and I'll see what he says.