magit-revert-popup: use shared sequencer actions

Use `magit-sequencer-{continue,skip,abort}' commands
shared with `magit-cherry-pick-popup' - there are no
`magit-revert-{continue,skip-abort}' commands.
move advice to auto-revert-handler to magit-blame.el

This avoids compile warnings.
magit.el: require magit-blame

Fixes #1462.
magit-refresh-buffer: remove unused internal variables
magit-restore-window-configuration: default to t
use --filter instead of cl-find{,-if}
magit-merge-warn-dirty-worktree: shorten doc-string
rename magit-{branches => refs}-buffer-name-format

When the branch-manager wazzup modes were merged into the new refs mode,
this variable was not adjusted accordingly.  We now adjust the symbol
name, value and doc-string.
remove magit-set-variable-and-refresh

Remove `magit-set-variable-and-refresh' which was used to set
various Custom options and the refresh some Magit buffers using
`magit-refresh-all'.  That no longer worked as expected because
the latter function now only refreshes Magit buffers in the current
repository.  So this function only had an effect in the repository
at ~/.emacs.d.
magit-auto-revert-mode-lighter: set :type custom property
change custom group of highlight options

Change the Custom group of options `magit-highlight-whitespace',
`magit-highlight-trailing-whitespace' and `magit-highlight-indentation'
from `magit' to `magit-diff'.
magit-restore-window-configuration: change custom group

Change `magit-restore-window-configuration's custom group from
`magit-modes' to the toplevel `magit'.  This is an important option
affecting everything.  It should therefor be featured very prominently.
magit-auto-revert-mode: change custom group

Change `magit-auto-revert-mode's custom group from `magit-modes' to the
toplevel `magit'.  Yes this is implemented as a mode, but it also is an
extremely important option with far reaching consequences, so it should
be featured very prominently.
magit-wip-ref-format: correct custom group
magit-wip: correct doc-string
magit-diff-options: correct custom group

Put `magit-diff-options' in Custom group `magit-popups' instead of
`magit'.  Do *not* put it in `magit-diff' because all equivalent
variables are currently placed in `magit-popups'.

(All of these variables, except for this one, are named
`magit-...-popup-defaults'.  We don't change the name of this variable
because the convention also isn't good.  All of these variables,
including this one, will be renamed at the same time).
magit-log-section-args: correct custom group
magit-popup-use-prefix-argument: correct custom group
magit-ellipsis: update doc-string, group and position

`magit-ellipsis' is no longer used in logs only.  Adjust the
doc-string and Custom group accordingly.  Also move the definition.
magit-ellipsis: define value literally

Now that we explicitly set the coding system
to utf-8 we can safely insert such characters.