Add flipme attribute to textboxclass

Instead of calculating the y-position of the text box when it's created,
we will store a flag that says whether or not the text box should be
flipped in Flip Mode (and thus stay right-side-up), and when it comes
time to draw the text box, we will check Flip Mode and calculate the
position then.

desktop_version/src/Textbox.h

@@ -43,6 +43,8 @@ public:
 
     int max;
 
+    /* Whether to flip text box y-position in Flip Mode. */
+    bool flipme;
 };
 
 #endif /* TEXTBOX_H */