Support hiding tray icons

[andresilva]

Adds support for hiding tray icon for specific apps:

"tray": {
	"icon-size": 21,
	"spacing": 10,
	"icons": {
		"blueman": "bluetooth",
		"TelegramDesktop": "$HOME/.local/share/icons/hicolor/16x16/apps/telegram.png",
		"spotify": false
	}
}

Tray icon for spotify will be hidden.

[alexhulbert]

Thanks for this PR, it works really well

[AntGarSil]

FYI I've done a similar thing here, just a different approach with less config required #4826