* Replace "Always_show_goals" with "Toggle_showing_goals"
The "Always_show_goals" flag is a no-op on anything other than a
training mission. This replaces it with a new flag which toggles
whether the goals are shown instead, in keeping with the existing
"Toggle_debriefing" flag.
* Rename other occurrences of Always_show_goals
* Update stale comment
* Update stale member names
* Remove unused #define