Move sysop notification settings from node to system level

The validation user (required new user feedback user number) and error notification/level settings don't make sense under node settings in today's world where all nodes typically run on the same system and serve the same BBS.

Moved from SCFG->Nodes->... Advanced Options to (new sub-menu) SCFG->System->Notifications. Likewise, these 3 settings (valuser, erruser, errlevel) were moved from node*/node.ini to ctrl/main.ini.

If you're already running v3.20a, then you'll want to make sure you set these in SCFG->System->Notifications how you prefer them as the migration (now handled in upgrade_to_v320.js) won't have been done for you automatically. The default is no-new-user-feedback required and no-error-notification user set.

Added a prompt to the SCFG setup wizard to prompt for this setting since it still is a FAQ.

Other cosmetic changes to SCFG help and setup wizard.