FRED has an autosave feature but it wasn't invoked in too many places. This adds autosaving whenever a major dialog is closed, unless it was closed by hitting Cancel. NB: Autosave is not yet implemented in qtFRED.
Also, `addvariabledlg` incorrectly referred to `OnOk` instead of `OnOK` and `CMessageEditorDlg` incorrectly referred to `OnOK` instead of `OnOk`, so this fixes those and distinguishes `OnOk` by renaming it `OnButtonOk` to be consistent with the event editor and other dialogs.
We need to call `UpdateData()` in the `OnOK()` function and in several other places so that the member variables are populated with the most recent input from the UI. This prevents certain input (such as Player Entry Delay changes) from being lost by being overwritten with stale stored values.
This fixes a bug reported by Kitsune where the Player Entry Delay box did not work properly. It also fixes the random checkbox issue from #5494.
This introduces a new mechanism for handling bit flags. Instead of using an int (or two, or three) to write bits into, this uses the std::bitset in a wrapper class that accepts an enum class as input. This means that certain classes of errors we've had a few of in the engine, where a coder used the wrong set of flags or checked them against the wrong variable (SF_STEALTH vs SIF_STEALTH, for example) can now be detected at a compiler level rather than not at all.
Goober5000