(TK-83) Add :enable-trailing-slash-redirect option

Add new :enable-trailing-slash-redirect option to the options map
for all service functions that add handlers. When true, all
requests made to the handler without a trailing slash will be
redirected to have a trailing slash. Defaults to false.
Nit - feel free to ignore.  I probably would have gone with passing this around everywhere in the "enable" form as read from the config rather than negating it internally.  "enabled?" reads a little cleaner to me than "disabled?".