(svn r1894) - Codechange: cleaned up the console a bit, wholly unified handling of text with that of editboxes

- Codechange: Introduction of Textbuf struct which not only holds physical data as length but also pixel-constrains (width) and information about the caret
- Codechange: Move Clipboard function to OS specific file. Currently only Windows has clipboard actions
- Feature: Editboxes, console and exit screen also accept the numeric-enter as a yes
- Feature: Navigation through text with cursor keys is possible, as well as arbitrary insertion (also paste) and deletion; both backspace and del keys. Functions DeleteTextBufferChar, InsertTextBufferChar and InsertTextBufferClipboard handle input and deletion. Navigation is done through MoveTextBufferPos.
- Fix: OTTD crash when opening 'add server' editbox
- CodeChange: fix up some stringwidth calculations in gfx.c. You can get the width in pixels of a character by calling GetCharacterWidth().

gfx.h

@@ -69,8 +69,10 @@ bool ChangeResInGame(int w, int h);
 void ToggleFullScreen(const bool full_screen);
 
 /* gfx.c */
+#define ASCII_LETTERSTART 32
 VARDEF int _stringwidth_base;
 VARDEF byte _stringwidth_table[0x2A0];
+static inline byte GetCharacterWidth(int key) { return _stringwidth_table[key - ASCII_LETTERSTART];}
 
 VARDEF DrawPixelInfo _screen;
 VARDEF DrawPixelInfo *_cur_dpi;