Spell-check in text boxes

Description

As mentioned in #4190 (comment 326248726), the use of Scintilla open the possibility of spell-checking. Would be nice to have it on the textbox of the "Text Parameters" dialog (maybe also in the page properties dialog).

It should follow some KiCad property of language that could be changed with out relation with the installation language. If possible, also use the LibreOffice dictionary already installed on Linux distributions.

KiCad Version

Application: KiCad
Version: 5.99.0-unknown-bdada70~88~ubuntu20.04.1, release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.68.0 OpenSSL/1.1.1d zlib/1.2.11 brotli/1.0.7 libidn2/2.2.0 libpsl/0.21.0 (+libidn2/2.2.0) libssh/0.9.3/openssl/zlib nghttp2/1.40.0 librtmp/2.3
Platform: Linux 5.4.0-21-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    Build date: Apr 12 2020 13:43:05
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
    Boost: 1.71.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.68.0
    Compiler: GCC 9.3.0 with C++ ABI 1013

Build settings:
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON