Add localization "foundation" (many code changes)

This commit adds most of the code changes necessary for making the game
translatable, but does not yet "unhardcode" nearly all of the strings
(except in a few cases where it was hard to separate added
loc::gettexts from foundational code changes, or all the localization-
related menus which were also added by this commit.)

This commit is part of rewritten history of the localization branch.
The original (unsquashed) commit history can be found here:
https://github.com/Dav999-v/VVVVVV/tree/localization-orig

desktop_version/src/Script.h

@@ -77,6 +77,8 @@ public:
 
     void run(void);
 
+    void translate_dialogue(void);
+
     void startgamemode(enum StartMode mode);
 
     void teleport(void);
@@ -99,6 +101,11 @@ public:
     int texty;
     int r,g,b;
     bool textflipme;
+    bool textcentertext;
+    size_t textpad_left;
+    size_t textpad_right;
+    size_t textpadtowidth;
+    char textcase;
 
     //Misc
     int i, j, k;