unbox all faces

Stop putting a box around all faces.  I assume these boxes where there
because until very recently changing the background color of the current
section to highlight it meant that all background colors of elements of
that section (such as refnames in logs) would lose their background
color.  That has been fixed now, such things are now propertized using
overlays which stay above the current-section-overlay.
use the same tag and branch faces in headers as elsewhere

Stop using the `magit-tag' and `magit-branch' faces in headers.  Now
that the `magit-log-head-label-*'s no longer need a box around them
(because the background color no longer gets overwritten by section
highlighting) we also no longer need alternative box-less faces.
(I suppose we had those because the boxed variants were "making the
headers to noisy", or something).

Remove these faces and instead use `magit-log-head-label-tags',
`magit-log-head-label-local', `magit-log-head-label-remote'.  The
prefixes of these faces are very silly, even if they were only used
in logs, which hasn't been the case for a long time now.  That will
be addresses in a later commit.  In fact `magit-log-head-label-tags'
will then be renamed to `magit-tag', completing the cycle.

Also note that we now use two distinct faces for local and remote in
headers too, just like we have done everywhere else for quite some time
That also means we no longer have to say something silly like "branch @
remote" and can instead just use "remote/branch" (again, you guessed it,
like everywhere else).
rename magit-ref{s => }-namespaces
magit-ref-namespace: add entry for stgit patches in magit-stgit.el
magit-log-head-label-patches: remove face

use `magit-stgit-patch' instead.
magit-mode: always set show-trailing-whitespace to nil

It might be that setting this to t "gives weird results"
when `magit-whitespace-warning-face' is different from
`trailing-whitespace', but it also does so when this is
not the case.
rename face magit-whitespace-warning{-face => }, move definition

Names of faces shouldn't end with "-face".  And this face has
nothing to do with the faces among which it used to be defined.
rename face magit-section-{title => heading}

That's the term we now use everywhere else.
rename faces magit-diff-{add,del,none => added,removed,context}

so that their names match those of the `diff-*' faces they inherit from.
rename faces whose names previously began with "magit-log-head-label-"

These faces have been used for things not related to logging for a long
time now.  Besides what is a "head label"?  Label kinda makes sense, but
there is but one HEAD.  Also rename `magit-log-sha1' to `magit-hash'.
Adjust some of the doc-strings accordingly.
Merge branch 'n/new-faces' into next