Editing reference designators in spreadsheet view is not possible

Description

Current behavior: I can open the properties dialog on a component and change its parameters, including its RD. In the spreadsheet view, I can edit all other parameters but not the RD. This makes it a pain to rename multiple components, and in particular it results in there being no way whatsoever to change the RDs of multiple instances of hierarchical sheets. Expected: RD should be editable just like the value, footprint, and the other properties.

Steps to reproduce

1. Annotate a schematic
2. Open spreadsheet view
3. Attempt to change a reference designator

KiCad Version

Application: Eeschema

Version: 5.99.0-unknown-652a59b78~104~ubuntu18.04.1, 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 4.15.0-115-generic x86_64, 64 bit, Little endian, wxGTK

Build Info:
	Date: Sep 16 2020 10:17:45
	wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.22
	Boost: 1.65.1
	OCE: 6.9.1
	Curl: 7.58.0
	ngspice: 32+
	Compiler: GCC 7.5.0 with C++ ABI 1011

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_SPICE=ON