Implemented gui_set_config() so a newly edited configuration is actually stored.

Still need to decide when to write the new config to disk, to really make it persistent.

Probably best at program exit, for a small tool such as this.
Save configuration on exit.

At the moment, there's no "dirty-flagging" so the config is always saved, which is a bit redundant but on the other hand very (very) fast.

This is the first commit with an actual persistent config system in place, neat!
Implemented the "autodetect on startup" option, so it really does what it says.

Not at all happy with the internals of config_get_autodetect_on_startup(), more magic strings. Yuck.