Config File Management

Added save option and checks for existence of options.
I'd agree in another case, but here since we have an ini-like format and arbitrary options, obliterating the config file and writing what's in memory makes sense.
I'm pretty sure it'd take more time and resources to do it the "clean" way and it won't change a thing for the result.
It's not an uncommon way to do things either, zdoom has similar use cases for settings (runtime changes and arbitrary options) and does exactly that.