Stop storing preferences and legacy flags in the saved game

- 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

doc/editor/Advanced.html

@@ -44,15 +44,15 @@ future that the shield has been taken.</p>
 
 <h2>Stuff Done Flags - the Specifics</h2>
 
-<p>But what are the Stuff Done Flags? Picture a grid of numbers, 300 wide and 50 high, all
-of which start at 0. These 15000 numbers are your Stuff Done Flags, and they are all set
+<p>But what are the Stuff Done Flags? Picture a grid of numbers, 350 wide and 50 high, all
+of which start at 0. These 17500 numbers are your Stuff Done Flags, and they are all set
 to 0 when the party starts a scenario (and are saved in the save file, which is how the
 game remembers what you've done already when the save file is opened).</p>
 
 <p>Stuff Done Flag are described by coordinates. Much as the coordinates of a spot of
 terrain are given by an X and Y value, a Stuff Done Flag has coordinates too. The first
-coordinate of a Stuff Done Flag is the column it is in (out of 300 columns, a number from
-0 to 299), and the second coordinate of a Stuff Done Flag is the row it is in (out of 50
+coordinate of a Stuff Done Flag is the column it is in (out of 350 columns, a number from
+0 to 349), and the second coordinate of a Stuff Done Flag is the row it is in (out of 50
 rows, a number from 0 to 49). For example, the taking of a shield may be attached to Stuff
 Done Flag X = 112, Y = 3, also written (112,3). Later chapters often refer to the two
 parts of a Stuff Done Flag (the X coordinate is the first part and the Y coordinate is the