(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().

window.h

@@ -222,13 +222,20 @@ enum {
 	WDP_CENTER = -2,
 };
 
+typedef struct Textbuf {
+	char *buf;                  /* buffer in which text is saved */
+	uint16 maxlength, maxwidth; /* the maximum size of the buffer. Maxwidth specifies screensize in pixels */
+	uint16 length, width;       /* the current size of the buffer. Width specifies screensize in pixels */
+	bool caret;                 /* is the caret ("_") visible or not */
+	uint16 caretpos;            /* the current position of the caret in the buffer */
+	uint16 caretxoffs;          /* the current position of the caret in pixels */
+} Textbuf;
+
 typedef struct {
 	StringID caption;
-	bool caret;
 	WindowClass wnd_class;
 	WindowNumber wnd_num;
-	uint16 maxlen, maxwidth;
-	char *buf;
+	Textbuf text;
 	const char* orig;
 } querystr_d;