[libami] add button, textbox and textinput from requestchoice/executecmd

Marcus had written up workbench style widgets inside the two external
helper programs requestchoice and executecmd.  This ports the code over
to libami.

Note that there isn't a generic gadget or collection of gadgets yet -
this is purely a refactor of the code, and the upcoming commit that
migrates requestchoice/executecmd over to use them just handles them
directly via xlib like they have always done.

libami/gadget_textbox.h

@@ -0,0 +1,35 @@
+#ifndef	__LIBAMI_GADGET_TEXTBOX_H__
+#define	__LIBAMI_GADGET_TEXTBOX_H__
+
+// These are for the text box widget
+#define TXT_HSPACE   48
+#define TXT_TOPSPACE 4
+#define TXT_MIDSPACE 3
+#define TXT_BOTSPACE 4
+
+struct gadget_textbox_line {
+	struct gadget_textbox_line *next;
+	const char *text;
+	int l, w, h;
+};
+
+struct gadget_textbox {
+	Display *dpy;
+	struct DrawInfo *dri;
+	GC gc;
+	Window w;
+	int x, y;
+	int width, height;
+
+	struct gadget_textbox_line *firstline, *lastline;
+};
+
+extern	struct gadget_textbox *gadget_textbox_create(Display *dpy,
+	    struct DrawInfo *dri, GC gc, Window mainwin, int x, int y,
+	    int width, int height);
+extern	void gadget_textbox_free(struct gadget_textbox *g);
+extern	struct gadget_textbox_line * gadget_textbox_addline(
+	    struct gadget_textbox *g, const char *text);
+extern	void gadget_textbox_refresh(struct gadget_textbox *g);
+
+#endif	/* __LIBAMI_GADGET_TEXTBOX_H__ */