Close project doesn't reset title bar

Description

Closing an open project leaves the path and filename of the project in the project manager title bar.

Steps to reproduce

1. Start KiCad
2. Open a project
3. Close the project

KiCad Version

Application: KiCad

Version: (5.99.0-2659-g211cbadc2), debug build

Libraries:
	wxWidgets 3.0.4
	libcurl/7.64.1 SecureTransport (LibreSSL/2.8.3) zlib/1.2.11 nghttp2/1.39.2

Platform: macOS Catalina Version 10.15.5 (Build 19F101), 64 bit, Little endian, wxMac

Build Info:
	Date: Aug 10 2020 19:39:22
	wxWidgets: 3.0.4 (wchar_t,STL containers,compatible with 2.8)
	Boost: 1.73.0
	OCE: 6.9.1
	Curl: 7.64.1
	ngspice: 32
	Compiler: Clang 11.0.0 with C++ ABI 1002

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_USE_OCE=ON
	KICAD_SPICE=ON
	KICAD_STDLIB_DEBUG=OFF
	KICAD_STDLIB_LIGHT_DEBUG=OFF
	KICAD_SANITIZE=OFF