Move this macro from cli.c to cli.h so apps can use it

Move this macro from cli.c to cli.h so apps can use it
without duplicating the macro or the code:

/*!
 * In many cases we need to print singular or plural
 * words depending on a count. This macro helps us e.g.
 *     printf("we have %d object%s", n, ESS(n));
 */
#define ESS(x) ((x) == 1 ? "" : "s")

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@47827 65c4cc65-6c06-0410-ace0-fbb531ad65f3