Move GENERAL options into [general] section

[kchibisov]

The fact that this section should be at the top is confusing for some users, thus make a dedicated section for it and write an automatic migration rules to move things into it.

Certain fields, like shell could be moved into other sections, like [terminal], however things like live_config_reload can not, and are enabled for the whole instance.

Maybe [instance] section could be used instead, but it feels not general enough.