top: extended 'scale_tics' function for Ctrl-E scaling

That normalization of the 'scale_tics' function in the
prior commit convinced me that I won't please everyone
with my arbitrary choices for the scaling transitions.

So, this patch will provide the users with a means for
setting their own scaling transition points with a new
toggle. Ctrl-E was chosen since the 'e/E' toggles were
already present as a means of scaling (albeit memory).

[ this toggle will also serve an educational purpose ]
[ by allowing one to see all the scaling conventions ]

The scaling a user establishes is saved in the rcfile.

Signed-off-by: Jim Warner <james.warner@comcast.net>

top/top_nls.c

@@ -644,7 +644,7 @@ static void build_uniq_nlstab (void) {
       "  V,v,F   . Toggle: '~1V~2' forest view; '~1v~2' hide/show children; '~1F~2' keep focused\n"
       "\n"
       "%s"
-      "  W,Y,!     Write config file '~1W~2'; Inspect other output '~1Y~2'; Combine Cpus '~1!~2'\n"
+      "  W,Y,!,^E  Write cfg '~1W~2'; Inspect '~1Y~2'; Combine Cpus '~1!~2'; Scale time ~1Ctrl~2+'~1E~2'\n"
       "  q         Quit\n"
       "          ( commands shown with '.' require a ~1visible~2 task display ~1window~2 ) \n"
       "Press '~1h~2' or '~1?~2' for help with ~1Windows~2,\n"