Behaviorally: This change makes it so that Enter will never cancel
a dialog, unless that dialog only contains info to be read. Escape
will never unpredictably be treated as Enter. And some dialogs without
Escape to cancel, now can be canceled with Escape.
A lot of this just refactors dialogs to define the cancel button
at the top, not as a hotkey on a cancel button deep in the XML.
I think this makes enter/escape behavior in dialogxml files more
legible at a glance.
- Nuke global preference variables (they're now fetched with get_xxx_pref whenever needed)
- Nuke magic SDFs that store preferences and other info
- The only preferences now stored in the saved game are those related to difficulty
- play_sound no longer takes an option repeat parameter, but instead takes a delay which will be used if sounds are disabled
- SDF array increased to 350x50
- When saving a legacy scenario, a dialog is shown to remind you to update and to allow you to clear the legacy flag
