Reload configuration file without restart (i.e. via SIGHUP)

[jpmckinney]

First mentioned in incomplete PR #186

[jpmckinney]

Not quite sure what the plan was for #186. The Application instantiates a bunch of classes, including the Launcher which tracks the running processes in memory in a dict. The main reason I wouldn't want to restart Scrapyd is to avoid losing track of those processes – if I can restart Scrapyd while keeping track of processes #521, I don't really need reloads. Seeing as the configuration file can change things like the bind address, I don't see a way to reload that doesn't basically restart the app... So, closing as there doesn’t seem to be an advantage to reloading.