Add textbox indexes, update trinket/crew textboxes

This adds an attribute to textboxclass to allow a text box to keep an
index that references another text box inside the graphics.textboxes
std::vector.

This is needed because the second text box of a "You have found a
shiny trinket!" or "You have found a lost crewmate!" pair of text boxes
explicitly relies on the height of the first text box. With this, I have
moved those text boxes over to the new text box translation system.

Since the update order now matters, I added a comment to
recomputetextboxes() that clarifies that the text boxes must be updated
in linear order, starting from 0.

desktop_version/src/Input.cpp

@@ -271,7 +271,8 @@ static void updatebuttonmappings(int bind)
 
 static void recomputetextboxes(void)
 {
-    /* Retranslate and reposition all text boxes. */
+    /* Retranslate and reposition all text boxes.
+     * WARNING: Needs to update in linear order, starting from 0. */
     for (size_t i = 0; i < graphics.textboxes.size(); i++)
     {
         graphics.textboxes[i].updatetext();