symbol editor: wrong "Item" column width auto-trim

Description

Current behavior: after symbol name change "Item" column width in symbol tree auto-adjusted to width of "item" header text, almost hiding cells contents.

Expected behavior: no any automatic width adjustments or trimming to longest symbol name in cells.

Screencast_2020-07-07_20_10_36

Steps to reproduce

• Open symbol editor, open symbol tree.
• Select any symbol from any library.
• Open symbol properties dialog
• Alter symbol name, press "OK"

KiCad Version

Application: LibEdit
Version: (5.99.0-2200-g98664ee71), release build
Libraries:
	wxWidgets 3.0.4
	libcurl/7.58.0 OpenSSL/1.1.1 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 5.4.0-39-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
	Build date: Jul  6 2020 18:19:33
	wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
	Boost: 1.65.1
	Curl: 7.58.0
	Compiler: GCC 7.5.0 with C++ ABI 1011

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