debian elpa-notmuch: ship elisp and .png from "make install"

debian elpa-notmuch: ship elisp and .png from "make install"

Rather than ship from the source directories, ship these files from
where they're installed by "make install".

This doesn't resolve all the dh_missing warnings yet (due to #946142),
but it leaves the last bit of that problem in the hands of the dh-elpa
package, and it's not due to notmuch's packaging any longer.

Note that notmuch-pkg.el is only relevant for elpa, so it was not
installed by "make install", and has to be extracted deliberately from
the source tree.

Note also that we now don't ship make-deps.el or rstdoc.el, as these
are build tools and don't belong in the deployed package.

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>