Misc custom group fixes

Misc custom group fixes

* cus-start.el (show-trailing-whitespace): Move to editing basics.
* faces.el (trailing-whitespace): Don't use whitespace-faces group.
* obsolete/old-whitespace.el (whitespace-faces): Remove group.
(whitespace-highlight): Move to whitespace group.

* comint.el (comint-source):
* pcmpl-linux.el (pcmpl-linux):
* shell.el (shell-faces):
* eshell/esh-opt.el (eshell-opt):
* international/ccl.el (ccl): Remove empty custom groups.

* completion.el (dynamic-completion-mode):
* jit-lock.el (jit-lock-debug-mode):
* minibuffer.el (completion-in-region-mode):
* type-break.el (type-break-mode-line-message-mode)
(type-break-query-mode):
* emulation/tpu-edt.el (tpu-edt-mode):
* progmodes/subword.el (global-subword-mode, global-superword-mode):
* progmodes/vhdl-mode.el (vhdl-electric-mode, vhdl-stutter-mode):
* term/vt100.el (vt100-wide-mode): Specify explicit :group.

* term/xterm.el (xterm): Change parent group to terminals.

* master.el (master): Remove empty custom group.
(master-mode): Remove unused :group argument.
* textmodes/refill.el (refill): Remove empty custom group.
(refill-mode): Remove unused :group argument.

* textmodes/rst.el (rst-compile-toolsets): Use rst-compile group.

* cedet/semantic/symref/list.el (semantic-symref-auto-expand-results)
(semantic-symref-results-mode-hook)
(semantic-symref-results-summary-function): Fix :group.

* erc/erc-list.el (erc-list):
* erc/erc-menu.el (erc-menu):
* erc/erc-ring.el (erc-ring): Define custom groups, for define-erc-module.

* gnus/shr-color.el (shr-color-visible-luminance-min)
(shr-color-visible-distance-min): Use shr-color group.

* url/url-news.el (url-news): Remove empty custom group.