* new dotvariable dotspacemacs-emacs-pdumper-executable-file
* new dotvariable dotspacemacs-emacs-dumper-dump-file
* dump emacs if dotspacemacs-emacs-pdumper-executable-file is non nil
* rename core-dump.el to core-dumper.el
* add function spacemacs/dump-emacs
* explicitly load core-dumper.el file in init.el
* asynchronously dump emacs if layer list has changed, see special buffer
*spacemacs-dumper* for the output.