Subsheets don't match multi-unit element annotations. (lp:#1788976)

Original report created by Seth Hillbrand (sethh)

When re-annotating a hierarchical schematic with multiple copies of the
same sub-sheet, we don't currently match units between copies of the same
sub-sheet but we should or at least have an option to allow it.

Right now, I have a schematic with 12 sub-sheets that are copies of each
other.  I need to re-order the units of a couple of quad-op amps.  Ideally,
changing the unit in one sheet would change the identical unit in all of
the copies of that sub-sheet.  Maybe the solution is a menu-option
(propagate multi-unit ordering?) that can synchronize the items.

Naively, I expected the annotation option "Reset existing annotations" to
clear the unit letters as well because we also have the option "Reset, but
keep order of multi-unit parts".  But it didn't and doesn't seem to have a
different action.  What am I missing here?

Application: kicad
Version: (5.0.0-rc3-3-g9d4ceff), release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.54.0 LibreSSL/2.0.20 zlib/1.2.11 nghttp2/1.24.0
Platform: Mac OS X (Darwin 17.6.0 x86_64), 64 bit, Little endian, wxMac
Build Info:
    wxWidgets: 3.0.4 (UTF-8,STL containers,compatible with 2.8)
    Boost: 1.67.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.51.0
    Compiler: Clang 8.0.0 with C++ ABI 1002

Build settings:
    USE_WX_GRAPHICS_CONTEXT=ON
    USE_WX_OVERLAY=ON
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_ACTION_MENU=OFF
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON

Original tags: eeschema