PCBNew: block flip should flip in place

[Leandro Heck]

Flip a footprint or text keep its position, however, flipping a group of objects does not keep the position of the group. The anchor reference should be the center of the group too like for a single component.

[Seth Hillbrand (sethh)]

Please include your KiCad version

[Leandro Heck (leoheck)]

Here it is.

Application: kicad
Version: 6.0.0-rc1-unknown-b95aa1a~84~ubuntu18.04.1, release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.58.0 OpenSSL/1.1.0g zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1 (+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3
Platform: Linux 4.15.0-25-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
    Boost: 1.65.1
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.58.0
    Compiler: GCC 7.3.0 with C++ ABI 1011

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

[KiCad Janitor (kicad-janitor)]

Fixed in revision b8a03be8698db69ba02c7a9f4eec461fe02f9372
https://git.launchpad.net/kicad/patch/?id=b8a03be8698db69ba02c7a9f4eec461fe02f9372