Synopsis: Change allout user configuration so auto-activation is controlled

Synopsis: Change allout user configuration so auto-activation is controlled
solely by customization `allout-auto-activation'.

(allout-auto-activation-helper) (allout-setup): New autoloads implement new
custom set procedure for allout-auto-activation.  Also, explicitly invoke
(allout-setup) after allout-auto-activation is custom-defined, to effect
the settings in emacs sessions besides the few where allout-auto-activation
customization is donea.
(allout-auto-activation): Use allout-auto-activation-helper to :set.
Revise the docstring.
(allout-init): Reduce functionality to just customizing
allout-auto-activation, and mark obsolete.
(allout-mode): Respect string values for allout-auto-activation.  Run
allout-after-copy-or-kill-hook without any args.
(allout-mode) (allout-layout) (allout-default-layout) (outlineify-sticky):
Adjust docstring for new scheme.
(allout-after-copy-or-kill-hook): No arguments - hook implementers should
concentrate on the kill ring.