Add Revert (aka: reload from disk) to PCBNew and Eeschema.

Description

It would be useful to have ability to refresh / reload *.kicad_sch file from disk, aka "F5" keyboard shortcut. This would be useful while editing schematic with text editor (for example - bulk change of text sizes by using regex in text editor..)

• I know, that bulk property change will be enabled by !484 (merged), but file reload will be useful anyway

Steps to reproduce

1. Open schematic;
2. Edit schematic with text editor;
3. eeschema.exe must be reopened to get latest changes from text editor;

KiCad Version

Application: Eeschema

Version: (5.99.0-7714-g70c397a9b4), release build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.71.0 OpenSSL/1.1.1g (Schannel) zlib/1.2.11 brotli/1.0.7 libidn2/2.3.0 libpsl/0.21.0 (+libidn2/2.3.0) libssh2/1.9.0 nghttp2/1.41.0

Platform: Windows 10 (build 19042), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Dec 20 2020 21:58:40
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8)
	Boost: 1.73.0
	OCE: 6.9.1
	Curl: 7.71.0
	ngspice: 32
	Compiler: GCC 10.2.0 with C++ ABI 1014

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