Resolve discrepancies related to allowing spaces in net names

Description

Net inspector throws an error that netnames cannot contain spaces, but one can create such netname using labels in eeschema. PCBnew should allow netnames with spaces.

Steps to reproduce

1. (included in screesnot), click "PLUS" button to add netname with space, between steps 2 and 3.

KiCad Version

Application: KiCad PCB Editor (64-bit)

Version: (5.99.0-12564-ga3dcdd4887), release build

Libraries:
	wxWidgets 3.1.5
	libcurl/7.78.0-DEV Schannel zlib/1.2.11

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

Build Info:
	Date: Sep 26 2021 21:01:14
	wxWidgets: 3.1.5 (wchar_t,wx containers)
	Boost: 1.76.0
	OCC: 7.5.0
	Curl: 7.78.0-DEV
	ngspice: 35
	Compiler: Visual C++ 1929 without C++ ABI

Build settings:
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON