Enable copying of errors and warning messages

When a warning or an error message pops up there is no obvious way to copy it to the clipboard.

https://i.imgur.com/yqJAhEd.png

In the example above there is no way to copy the message. It doesn't show up as a console message either.

Application: KiCad

Version: (5.99.0-7213-g4f651901a), release build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.73.0 OpenSSL/1.1.1h zlib/1.2.11 zstd/1.4.5 libidn2/2.3.0 libpsl/0.21.1 (+libidn2/2.3.0) libssh2/1.9.0 nghttp2/1.41.0

Platform: Linux 5.9.9-arch1-1 x86_64, 64 bit, Little endian, wxGTK, KDE, x11

Build Info:
	Date: Nov 27 2020 20:35:48
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.72.0
	OCC: 7.5.0
	Curl: 7.73.0
	ngspice: 33
	Compiler: GCC 10.2.0 with C++ ABI 1014

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
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON