Add a command search tool

Description

Not an issue, feature request

The requested feature is to add a search tool for commands. This could be quite similar to the already existent "List hotkeys..." in the nightly and in fact could be just a modified version to allow executing commands not only finding their hotkey. It would a nice addition to the existing tool, because not every command has a shortcut or the user might have forgotten it (which forces them to close the window and press the hotkey)

Such feature would improve the user's workflow, because they don't have to search through menus and icons to find the required command and it is generally faster than pointing and clicking

Steps to reproduce

1. N/a

KiCad Version

Version: 5.99.0-unknown-d70cebcd62~115~ubuntu20.04.1, release build

Libraries:
	wxWidgets 3.0.4
	libcurl/7.68.0 OpenSSL/1.1.1f 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 5.6.0-1042-oem x86_64, 64 bit, Little endian, wxGTK, budgie-desktop, x11

Build Info:
	Date: Feb  7 2021 08:04:14
	wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.71.0
	OCC: 7.3.0
	Curl: 7.68.0
	ngspice: 31
	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
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON