"New colors last"; place colors at end of New

New option to place color palette items at the end of the "New"
dialog, rather than at the beginning.  Useful for when users
would want to pick from a set of Starters and/or Templates,
e.g., in a school or museum environment.

Available via command-line option "--newcolorslast", and
config file setting "newcolorslast=yes".  (And anti-option to
override config file settings, "--newcolorsfirst" and "...=no",
which represents the original behavior, which continues to be
the default).

Suggested by Bernard Verhaeghe.

docs/en/OPTIONS.txt

@@ -1,12 +1,12 @@
                                    Tux Paint
-                                version 0.9.23c
+                                 version 0.9.24
 
 Options Documentation
 
         Copyright (c) 2002-2018 by various contributors; see AUTHORS.txt
                             http://www.tuxpaint.org/
 
-                                October 7, 2018
+                               December 18, 2018
 
      ----------------------------------------------------------------------
 
@@ -358,6 +358,10 @@ Windows Users
                Disables the Label tool: the tool that allows text entry which
                can be edited later.
 
+       newcolorslast=yes
+               Places the blank color options in the New dialog at the end,
+               so that any Starters and/or Templates are shown first.
+
        mirrorstamps=yes
 
                For stamps that can be mirrored, this option sets them to
@@ -980,6 +984,7 @@ Windows Users
          --nostampcontrols
          --nomagiccontrols
          --nolabel
+         --newcolorslast
          --mouse-accessibility
          --onscreen-keyboard
          --onscreen-keyboard-layout
@@ -1050,6 +1055,7 @@ Windows Users
          --stampcontrols
          --magiccontrols
          --label
+         --newcolorsfirst
          --nosysfonts
          --currentlocalefont
          --dontmirrorstamps