magit-stash-at-point: remove unused argument GET-NUMBER
magit-tag-at-point: new function
magit-read-tag: default to tag at point
magit-show-commit: support tags

Teach `magit-show-commit' how to show the commit tagged by the tag at
point.  This doesn't show the tag, it shows the tagged commit, even
for annotated tags.
magit-insert-tags: set the value of tag sections
magit-tag-section-map: new keymap

Bind the commands `magit-show-commit' and `magit-tag-delete'.
magit-confirm: when PROMPT contains "%i", don't append "%i files"

This allows using `magit-confirm' to confirm an action on multiple
non-file items without the generated prompt claiming we are acting
on files.  This is a kludge; once we use this more, we'll probably
do it differently.

Make use of this in `magit-stash-drop'.
magit-current-sections: new function

Add new function `magit-current-sections' as a variant of
`magit-section-region-siblings'.  If the region isn't active it returns
a list with just one member, the current section.  This is a bit of a
kludge, and it likely will be replaced with a better approach
eventually, see #1321.

Use use of this in `magit-sequencer-read-args', `magit-am-apply-patches'
and `magit-format-patch'.
magit-tag-delete: support deleting multiple tags
Merge branch 'n/delete-tags' into next